#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define REP(i,n) for(long long i = 0; i < (n); i++)
#define FOR(i, m, n) for(long long i = (m);i < (n); ++i)
#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);

template<class T> using V = vector<T>;
template<class T, class U> using P = pair<T, U>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQR = priority_queue<T,vector<T>,greater<T>>;

constexpr ll MOD = (ll)1e9 + 7;
constexpr ll MOD2 = 998244353;
constexpr ll HIGHINF = (ll)1e18;
constexpr ll LOWINF = (ll)1e15;
constexpr long double PI = 3.1415926535897932384626433;

template<typename T> vector<T> make_v(size_t N,T init){return vector<T>(N,init);}
template<typename... T> auto make_v(size_t N,T... t){return vector<decltype(make_v(t...))>(N,make_v(t...));}
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template <class T, class U>ostream &operator<<(ostream &o, const map<T, U>&obj) {o << "{"; for (auto &x : obj) o << " {" << x.first << " : " << x.second << "}" << ","; o << " }"; return o;}
template <class T>ostream &operator<<(ostream &o, const set<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const multiset<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const vector<T>&obj) {o << "{"; for (int i = 0; i < (int)obj.size(); ++i)o << (i > 0 ? ", " : "") << obj[i]; o << "}"; return o;}
template <class T, class U>ostream &operator<<(ostream &o, const pair<T, U>&obj) {o << "{" << obj.first << ", " << obj.second << "}"; return o;}
template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
void print(void) {cout << endl;}
template <class Head> void print(Head&& head) {cout << head;print();}
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) {cout << head << " ";print(forward<Tail>(tail)...);}
template <class T> void chmax(T& a, const T b){a=max<T>(a,b);}
template <class T> void chmin(T& a, const T b){a=min<T>(a,b);}
void YN(bool flg) {cout << ((flg) ? "YES" : "NO") << endl;}
void Yn(bool flg) {cout << ((flg) ? "Yes" : "No") << endl;}
void yn(bool flg) {cout << ((flg) ? "yes" : "no") << endl;}


class Tree {
public:
	int N, MAX_bit;
	vector<vector<int>> edge;
	vector<int> depth;
	vector<int> order;
	vector<vector<int>> parent;
	vector<vector<int>> child;
	vector<vector<int>> descendant;


	Tree(int N, int MAX_bit = 20) :N(N), MAX_bit(MAX_bit), edge(N), depth(N, -1), order(N, -1), parent(N, vector<int>(MAX_bit)), child(N), descendant(N){
		//do nothing
	}

	//O(1)
	void make_edge(int from, int to) {
		edge[from].push_back(to);
	}

	//O(N)
	void make_depth(int root) {
		queue<int> q;
		depth[root] = 0;
		q.push(root);
		while (q.size()) {
			int from = q.front();
			q.pop();
			for (auto to : edge[from]) {
				if (depth[to] != -1) continue;
				depth[to] = depth[from] + 1;
				q.push(to);
			}
		}
	}

	//O(NlogN)
	void make_order(){
		vector<pair<int,int>> tmp(N);
		for (int i = 0; i < N; ++i) tmp[i] = {depth[i],i};
		sort(tmp.begin(),tmp.end(),greater<>());
		for (int i = 0; i < N; ++i) order[i] = tmp[i].second;
	}

	//O(MAX_bit*N)
	void make_parent() {
		for (int i = 0; i < N; ++i) parent[i][0] = i;
		for (int i = 0; i < N; ++i) for (auto j : edge[i]) if (depth[i] > depth[j]) parent[i][0] = j;
		for (int bit = 1; bit < MAX_bit; ++bit) for (int i = 0; i < N; ++i) parent[i][bit] = parent[parent[i][bit - 1]][bit - 1];
	}

	//O(N)
	void make_child() {
		for (int i = 0; i < N; ++i) for (auto j : edge[i]) if (depth[i] < depth[j]) child[i].push_back(j);
	}

	//O(N^2)
	void make_descendant() {
		for (int i = 0; i < N; ++i) descendant[i].push_back(i);
		for (int i = 0; i < N; ++i) for (auto j : edge[order[i]]) if (depth[order[i]] < depth[j]) for(auto k: descendant[j]) descendant[order[i]].push_back(k);
	}

	//O(MAX_bit*logN) Lowest_Common_Ancestor
	int LCA(int l, int r) {
		if (depth[l] < depth[r]) swap(l, r);
		int diff = depth[l] - depth[r];
		for (int bit = 0; bit < MAX_bit; ++bit) if (diff & (1 << bit)) l = parent[l][bit];
		
		int ok = (1 << MAX_bit), ng = -1, md;
		while (ok - ng>1) {
			md = (ok + ng) / 2;
			int x = l, y = r;
			for (int bit = 0; bit < MAX_bit; ++bit) if (md & (1 << bit)) x = parent[x][bit];
			for (int bit = 0; bit < MAX_bit; ++bit) if (md & (1 << bit)) y = parent[y][bit];
			(x == y ? ok : ng) = md;
		}
		for (int bit = 0; bit < MAX_bit; ++bit) if (ok & (1 << bit)) l = parent[l][bit];
		return l;
	}

	void print() {
		cout << " depth { " << depth[0];
		for (int i = 1; i < N; ++i) cout << ", " << depth[i];
		cout << " }" << endl;

		cout << "parent { " << parent[0][0];
		for (int i = 1; i < N; ++i) cout << ", " << parent[i][0];
		cout << " }" << endl;

		cout << " child { " << child[0];
		for (int i = 1; i < N; ++i) cout << ", " << child[i];
		cout << " }" << endl;

		cout << "descen { " << descendant[0];
		for (int i = 1; i < N; ++i) cout << ", " << descendant[i];
		cout << " }" << endl;
	}

};


//Combination Mod
class Combination_Mod {
public:
	vector<long long> fac,finv,inv;
	long long MOD;

	Combination_Mod(int N,long long mod) : fac(vector<long long>(N + 1)), finv(vector<long long>(N + 1)), inv(vector<long long>(N + 1)), MOD(mod) {
		fac[0] = fac[1] = finv[0] = finv[1] = inv[1] = 1;
		for (int i = 2; i <= N; ++i) {
			fac[i] = fac[i - 1] * i % MOD;
			inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
			finv[i] = finv[i - 1] * inv[i] % MOD;
		}
	}
	
	long long num(int n, int k) {
		return ((n < 0 || k < 0 || n < k) ? 0 : fac[n] * (finv[k] * finv[n - k] % MOD) % MOD);
	}
};


//Factorial_Mod
vector<long long> Factorial_Mod(long long N, long long mod) {
    vector<long long> res(N + 1, 1);
    for (long long i = 1; i <= N; ++i) res[i] = (res[i - 1] * i) % mod;
    return res;
}

int main() {
    ll N,K; cin >> N >> K;
    corner(N==1,K);
    corner(K==1,0);
    
    Tree tree(N);
    for(int i = 0; i < N-1; ++i){
        int a,b; cin >> a >> b;
        a--,b--;
        tree.make_edge(a,b);
        tree.make_edge(b,a);
    }
    tree.make_depth(0);
    tree.make_order();
    tree.make_child();
    Combination_Mod CM(N+K,MOD);
    auto F = Factorial_Mod(N+K,MOD);

    

    ll ans = K;
    for(int i = 0; i < 1; ++i){
        ll M = tree.child[i].size();
        if(M==0) continue;
        (ans *= CM.num(K-1,M)) %= MOD;
        (ans *= F[M]) %= MOD;
    }
    for(int i = 1; i < N; ++i){
        ll M = tree.child[i].size();
        if(M==0) continue;
        (ans *= CM.num(K-2,M)) %= MOD;
        (ans *= F[M]) %= MOD;
    }
    cout << ans << endl;

    return 0;
}


Measured memory_bytes: 30608