#define KAKUSUKO
#include <iostream>
#include <algorithm>
#include <bitset>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <cstring>
#include <utility>
#include <vector>
#include <complex>
#include <valarray>
#include <fstream>
#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <numeric>
#include <climits>
#include <random>

#define _overload(a, b, c, d, ...) d
#define _rep1(X, A, Y) for (int (X) = (A);(X) <= (Y);++(X))
#define _rep2(X, Y) for (int (X) = 0;(X) < (Y);++(X))
#define rep(...) _overload(__VA_ARGS__, _rep1, _rep2)(__VA_ARGS__)
#define rrep(X,Y) for (int (X) = Y-1;(X) >= 0;--(X))
#define all(X) (X).begin(),(X).end()
#define len(X) ((int)(X).size())
#define mod(n, m) (((n)%(m)+(m))%m)
#define fi first
#define sc second
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> Pii;
typedef pair<ll,ll> Pll;
const int INFINT = 1 << 30;                          // 1.07x10^ 9
const ll INFLL = 1LL << 60;                          // 1.15x10^18
const double EPS = 1e-10;
const int MOD = 1000000007;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

const int MAX_N = 100000;
int N, K;
int a[MAX_N], b[MAX_N];
                            
struct edge { int to, cost; };
const int MAX_V = MAX_N, INF = 1e9;

// Vの初期化を忘れない。
int V;
vector<edge> G[MAX_V];
int d[MAX_V];

void add_edge(int v, int u, int cost) {
  G[v].push_back((edge){u, cost});
  G[u].push_back((edge){v, cost});
}

void dijkstra(int s) {
  fill(d, d+V, INF);
  priority_queue<Pii, vector<Pii>, greater<Pii> > pque;
  d[s] = 0;
  pque.push(Pii(0, s));


  while (!pque.empty()) {
    Pii p = pque.top(); pque.pop();
    int v = p.second;
    if (d[v] < p.first) continue;
    for (int i = 0; i < (int)G[v].size(); ++i) {
      edge e = G[v][i];
      if (d[e.to] > d[v] + e.cost) {
        d[e.to] = d[v] + e.cost; 
        pque.push(Pii(d[v]+ e.cost, e.to));
      }
    }
  }
}


int childCount[MAX_N];

void rec(int v) {
  for (int i = 0; i < G[v].size(); ++i) {
    int u = G[v][i].to;
    if (d[v] < d[u]) {
      ++childCount[v];
      rec(u);
    }
  }
}


ll fact[MAX_N+1];
ll inv_fact[MAX_N+1];

//整数a,bに対し、ax + by = gcd(a,b) を満たす整数x,y,gcd(a,b) を計算する
ll extgcd(ll a, ll b, ll& x, ll& y) {
  ll d = a;
  if (b != 0) {
    d = extgcd(b, a%b, y, x);
    y -= (a/b) * x;
  } else {
    x = 1; y = 0;
  }
  return d;
}

//ax ≡ gcd(a,m) (mod m) を満たすxを計算する。
ll mod_inverse(ll a, ll m) {
  ll x, y;
  extgcd(a, m, x, y);
  return (m + x%m) % m;
}


void init(ll n, ll mod) {
  fact[0] = 1;
  for (int i = 1; i <= n; ++i) fact[i] = (fact[i-1]*i)%mod;

  for (int i = 0; i <= n; ++i) inv_fact[i] = mod_inverse(fact[i], mod);
}

ll mod_comb(ll n, ll r, ll mod) {
  return fact[n]*inv_fact[r]%mod*inv_fact[n-r]%mod;
}

void rec2(int v, ll& ans) {
  if (childCount[v] == 0) return;
  if (v == 0) {
    if (K-1 < childCount[v]) {
      ans = 0;
    } else {
      ans = mod(ans*fact[K-1]%MOD*inv_fact[K-1-childCount[v]], MOD);
    }
  } else {
    if (K-2 < childCount[v]) {
      ans = 0;
    } else {
      ans = mod(ans*fact[K-2]%MOD*inv_fact[K-2-childCount[v]], MOD);
    }
  }
  for (int i = 0; i < G[v].size(); ++i) {
    int u = G[v][i].to;
    if (d[v] < d[u]) {
      rec2(u, ans);
    }
  }
}


int main() {
  std::ios::sync_with_stdio(false);std::cin.tie(0);

  cin >> N >> K;
  rep(i, N-1) cin >> a[i] >> b[i];
  rep(i, N-1) { --a[i]; --b[i]; }
  V = N;
  init(K, MOD);

  rep(i, N-1) {
    add_edge(a[i], b[i], 1);
  }

  dijkstra(0);
  rec(0);
  
  ll ans = K;
  cerr << ans << endl;
  rec2(0, ans);

  cout << ans << endl;
  return 0;
}


Measured memory_bytes: 11124