Buggy python submission (verdict: Runtime Error):
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
def dfs(p, v):
    s = 0
    for nv in G[v]:
        if nv == p:
            continue
        res = dfs(v, nv)
        cnt[v].append(res)
        s+=res
    cnt[v].append(N-s-1)
dfs(-1, 0) 


Fixed submission:
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
que = [0]
depth = [-1]*N
depth[0] = 0
while que:
    v = que.pop()
    d = depth[v]
    for nv in G[v]:
        if depth[nv]>=0:
            continue
        depth[nv] = d+1
        que.append(nv)
d_to_i = [[] for _ in range(N)]
for i in range(N):
    d_to_i[depth[i]].append(i)
for d in range(N)[::-1]:
    for v in d_to_i[d]:
        for nv in G[v]:
            if depth[nv]<depth[v]:
                continue
            if cnt[nv]:
                cnt[v].append(sum(cnt[nv])+1)
            else:
                cnt[v].append(1)
for i in range(N):
    res = N-1
    for j in cnt[i]:
        res-=j
    cnt[i].append(res)
ans = 0
p = [1]*N
for i in range(1, N):
    p[i] = p[i-1]*2%mod
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = p[N-1]-1
    for a in cnt[v]:
        res-=p[a]-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)

Buggy python submission (verdict: Time Limit Exceeded):
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
def dfs(p, v, n):
    s = 0
    for nv in G[v]:
        if nv == p:
            continue
        res = dfs(v, nv, n+1)
        cnt[v].append(res)
        s+=res
    cnt[v].append(N-s-1)
    return s+1
dfs(-1, 0, 0) 
ans = 0
p = [1]*N
for i in range(1, N):
    p[i] = p[i-1]*2%mod
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = p[N-1]-1
    for a in cnt[v]:
        res-=p[a]-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)







Fixed submission:
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
que = [0]
depth = [-1]*N
depth[0] = 0
while que:
    v = que.pop()
    d = depth[v]
    for nv in G[v]:
        if depth[nv]>=0:
            continue
        depth[nv] = d+1
        que.append(nv)
d_to_i = [[] for _ in range(N)]
for i in range(N):
    d_to_i[depth[i]].append(i)
for d in range(N)[::-1]:
    for v in d_to_i[d]:
        for nv in G[v]:
            if depth[nv]<depth[v]:
                continue
            if cnt[nv]:
                cnt[v].append(sum(cnt[nv])+1)
            else:
                cnt[v].append(1)
for i in range(N):
    res = N-1
    for j in cnt[i]:
        res-=j
    cnt[i].append(res)
ans = 0
p = [1]*N
for i in range(1, N):
    p[i] = p[i-1]*2%mod
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = p[N-1]-1
    for a in cnt[v]:
        res-=p[a]-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)

Buggy python submission (verdict: Time Limit Exceeded):
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
que = [0]
depth = [-1]*N
depth[0] = 0
while que:
    v = que.pop()
    d = depth[v]
    for nv in G[v]:
        if depth[nv]>=0:
            continue
        depth[nv] = d+1
        que.append(nv)
d_to_i = [[] for _ in range(N)]
for i in range(N):
    d_to_i[depth[i]].append(i)
for d in range(N)[::-1]:
    for v in d_to_i[d]:
        for nv in G[v]:
            if depth[nv]<depth[v]:
                continue
            if cnt[nv]:
                cnt[v].append(sum(cnt[nv])+1)
            else:
                cnt[v].append(1)
for i in range(N):
    res = N-1
    for j in cnt[i]:
        res-=j
    cnt[i].append(res)
ans = 0
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = pow(2, N-1, mod)-1
    for a in cnt[v]:
        res-=pow(2, a, mod)-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)







Fixed submission:
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
que = [0]
depth = [-1]*N
depth[0] = 0
while que:
    v = que.pop()
    d = depth[v]
    for nv in G[v]:
        if depth[nv]>=0:
            continue
        depth[nv] = d+1
        que.append(nv)
d_to_i = [[] for _ in range(N)]
for i in range(N):
    d_to_i[depth[i]].append(i)
for d in range(N)[::-1]:
    for v in d_to_i[d]:
        for nv in G[v]:
            if depth[nv]<depth[v]:
                continue
            if cnt[nv]:
                cnt[v].append(sum(cnt[nv])+1)
            else:
                cnt[v].append(1)
for i in range(N):
    res = N-1
    for j in cnt[i]:
        res-=j
    cnt[i].append(res)
ans = 0
p = [1]*N
for i in range(1, N):
    p[i] = p[i-1]*2%mod
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = p[N-1]-1
    for a in cnt[v]:
        res-=p[a]-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)

Buggy python submission (verdict: Time Limit Exceeded):
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
def dfs(p, v, n):
    s = 0
    for nv in G[v]:
        if nv == p:
            continue
        res = dfs(v, nv, n+1)
        cnt[v].append(res)
        s+=res
    cnt[v].append(N-s-1)
    return s+1
dfs(-1, 0, 0) 

ans = 0
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = pow(2, N-1, mod)-1
    for a in cnt[v]:
        res-=pow(2, a, mod)-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)







Fixed submission:
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
que = [0]
depth = [-1]*N
depth[0] = 0
while que:
    v = que.pop()
    d = depth[v]
    for nv in G[v]:
        if depth[nv]>=0:
            continue
        depth[nv] = d+1
        que.append(nv)
d_to_i = [[] for _ in range(N)]
for i in range(N):
    d_to_i[depth[i]].append(i)
for d in range(N)[::-1]:
    for v in d_to_i[d]:
        for nv in G[v]:
            if depth[nv]<depth[v]:
                continue
            if cnt[nv]:
                cnt[v].append(sum(cnt[nv])+1)
            else:
                cnt[v].append(1)
for i in range(N):
    res = N-1
    for j in cnt[i]:
        res-=j
    cnt[i].append(res)
ans = 0
p = [1]*N
for i in range(1, N):
    p[i] = p[i-1]*2%mod
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = p[N-1]-1
    for a in cnt[v]:
        res-=p[a]-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)

Buggy python submission (verdict: Time Limit Exceeded):
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
def dfs(p, v, n):
    s = 0
    for nv in G[v]:
        if nv == p:
            continue
        res = dfs(v, nv, n+1)
        cnt[v].append(res)
        s+=res
    cnt[v].append(N-s-1)
    return s+1
dfs(-1, 0, 0) 

ans = 0
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = pow(2, N-1, mod)-1
    for a in cnt[v]:
        res-=pow(2, a, mod)-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)







Fixed submission:
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
que = [0]
depth = [-1]*N
depth[0] = 0
while que:
    v = que.pop()
    d = depth[v]
    for nv in G[v]:
        if depth[nv]>=0:
            continue
        depth[nv] = d+1
        que.append(nv)
d_to_i = [[] for _ in range(N)]
for i in range(N):
    d_to_i[depth[i]].append(i)
for d in range(N)[::-1]:
    for v in d_to_i[d]:
        for nv in G[v]:
            if depth[nv]<depth[v]:
                continue
            if cnt[nv]:
                cnt[v].append(sum(cnt[nv])+1)
            else:
                cnt[v].append(1)
for i in range(N):
    res = N-1
    for j in cnt[i]:
        res-=j
    cnt[i].append(res)
ans = 0
p = [1]*N
for i in range(1, N):
    p[i] = p[i-1]*2%mod
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = p[N-1]-1
    for a in cnt[v]:
        res-=p[a]-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)

Buggy python submission (verdict: Runtime Error):
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
def dfs(p, v, n):
    s = 0
    for nv in G[v]:
        if nv == p:
            continue
        res = dfs(v, nv, n+1)
        cnt[v].append(res)
        s+=res
    cnt[v].append(N-s-1)
    return s+1
dfs(-1, 0, 0) 

ans = 0
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = pow(2, N-1, mod)-1
    for a in cnt[v]:
        res-=pow(2, a, mod)-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)







Fixed submission:
import sys 
sys.setrecursionlimit(10**9)
N = int(input())
G = [[] for _ in range(N)]
mod = 10**9+7
for _ in range(N-1):
    A, B = map(int, input().split())
    G[A-1].append(B-1)
    G[B-1].append(A-1)
cnt = [[] for _ in range(N)]
que = [0]
depth = [-1]*N
depth[0] = 0
while que:
    v = que.pop()
    d = depth[v]
    for nv in G[v]:
        if depth[nv]>=0:
            continue
        depth[nv] = d+1
        que.append(nv)
d_to_i = [[] for _ in range(N)]
for i in range(N):
    d_to_i[depth[i]].append(i)
for d in range(N)[::-1]:
    for v in d_to_i[d]:
        for nv in G[v]:
            if depth[nv]<depth[v]:
                continue
            if cnt[nv]:
                cnt[v].append(sum(cnt[nv])+1)
            else:
                cnt[v].append(1)
for i in range(N):
    res = N-1
    for j in cnt[i]:
        res-=j
    cnt[i].append(res)
ans = 0
p = [1]*N
for i in range(1, N):
    p[i] = p[i-1]*2%mod
for v in range(N):
    if len(cnt[v])<=1:
        continue    
    res = p[N-1]-1
    for a in cnt[v]:
        res-=p[a]-1
    ans+=res
    ans%=mod
inv = pow(2, (mod-2)*N, mod)
print(ans*inv%mod)