#include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os, const map<T,U>& mp){ os << "{"; for(auto& p : mp){ os << p << ","; } os << "}"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

#define MAX_N 200002

// x^n
long long mod_pow(long long x,long long n,long long MOD=1000000007LL){
    long long res=1;
    while(n){
        if(n&1) res=(res*x)%MOD;
        x=(x*x)%MOD;
        n>>=1;
    }
    return res;
}

// x^-1
long long mod_inv(long long x,long long MOD=1000000007LL){
    return mod_pow(x,MOD-2);
}

// x + y
long long mod_add(long long x,long long y,long long MOD=1000000007LL){
    return (x+y)%MOD;
}

// x-y
long long mod_sub(long long x,long long y,long long MOD=1000000007LL){
    return (x-y+MOD)%MOD;
}

// x * y
long long mod_mul(long long x, long long y, long long MOD=1000000007LL){
    return x * y % MOD;
}

// x / y
long long mod_div(long long x,long long y,long long MOD=1000000007LL){
    return x * mod_inv(y,MOD) % MOD;
}


ll fact[MAX_N];             // N!
ll fact_inv[MAX_N]; // N!の逆元
// O(log mod)で x^-1 を計算(法をmodとする)
ll invp(ll x,ll mod){
    return mod_pow(x,mod-2,mod);
}

// 法をmodとして組み合わせ nCrを計算(O(1))
ll nCr(ll n,ll r,ll mod){
    ll ret = fact[n];
    ret = (ret * fact_inv[r]) % mod;
    ret = (ret * fact_inv[n-r]) % mod;
    return ret;
}

// 初期化 O(MAX_N * log(mod)) くらいかなぁ
void init(ll MOD=mod){
    fact[0]=1;
    for(int i=1;i<MAX_N;i++) fact[i]=(fact[i-1]*i)%MOD;
    for(int i=0;i<MAX_N;i++) fact_inv[i]=invp(fact[i],MOD);
}


vector<int> G[100005];
vector<int> Tree[100005];
bool visit[100005];
void dfs(int me,int p){
    visit[me] = true;
    for(int c : G[me]){
        if(c==p || visit[c]) continue;
        Tree[me].push_back(c);
        dfs(c,me);
    }
}

int main(){
    ll N,K; cin >> N >> K;

    rep(i,N-1){
        int a,b; cin >> a >> b;
        a--;b--;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    dfs(0,-1);
    init();
    ll ans =  1;

    rep(i,N){
        ll c = Tree[i].size();
        ll ng = 2;
        if(i==0) ng--;
        if(K-ng-c<0){
            cout << 0 << endl;
            return 0;
        }
        ll t = mod_div(fact[K-ng],fact[K-ng-c]);
        ans *= t;
        ans %= mod;
    }

    /* ans *= fact[K]; */
    ans *= K;
    ans %= mod;
    cout << ans << endl;
}


Measured memory_bytes: 19072