//{{{
#include<algorithm>
#include<cmath>
#include<fstream>
#include<iomanip>
#include<iostream>
#include<map>
#include<numeric>
#include<queue>
#include<random>
#include<set>
#include<sstream>
#include<sys/time.h>
#include<unordered_map>
#include<unordered_set>
#include<vector>
using ll = long long;
enum : int { M = (int)1e9 + 7 };
enum : ll { MLL = (ll)1e18L + 9 };
using namespace std;
#ifdef LOCAL
#include"rprint2.hpp"
#else
#define FUNC(name) template <ostream& out = cout, class... T> void name(T&&...){ }
FUNC(prints) FUNC(printw) FUNC(printwe) FUNC(printb) FUNC(printbe) FUNC(printd) FUNC(printde) FUNC(printdu);
#endif
template <class S, class T>
istream& operator >> (istream& in, pair<S, T>& p){ return in >> p.first >> p.second; }
template <class T>
istream& operator >> (istream& in, vector<T>& v){ for(auto& e : v){ in >> e; } return in; }
//}}}

template <int M>
struct ModInt {
    int num;
    ModInt(): num(0){ }
    ModInt(int num): num(num){ }
    operator int () const { return num; }
    // template <class T> ModInt operator + (T n) const { n += num; return n >= M ? n - M : n; }
    // template <class T> ModInt operator - (T n) const { n = num - n; return n < 0 ? n + M : n; }
    template <class T> ModInt operator + (T n) const { auto ret = num + n; return ret >= M ? ret - M : ret; }
    template <class T> ModInt operator - (T n) const { auto ret = num - n; return ret < 0 ? ret + M : ret; }
    // template <class T> ModInt operator + (T n) const { return (num + n) % M; }
    // template <class T> ModInt operator - (T n) const { return (num - n + M) % M; }
    template <class T> ModInt operator * (T n) const { return (ll)num * n % M; }
    template <class T> ModInt operator / (T n) const { return (ll)num * modInv(ModInt(n)) % M; }
    template <class T> ModInt operator >> (T n) const { return num >> n; }
    template <class T> ModInt operator << (T n) const { return ((ll)num << n) % M; }
    template <class T> ModInt operator | (T n) const { return num | n; }
    template <class T> ModInt operator & (T n) const { return num & n; }
    template <class T> bool operator < (T n) const { return num < n; }
    template <class T> bool operator > (T n) const { return num > n; }
    template <class T> bool operator <= (T n) const { return num <= n; }
    template <class T> bool operator >= (T n) const { return num >= n; }
    template <class T> bool operator == (T n) const { return num == n; }
    template <class T> bool operator != (T n) const { return num != n; }
    ModInt operator ++ (int){ int ret = num; num = num == M + 1 ? 0 : num + 1; return ret; }
    ModInt operator -- (int){ int ret = num; num = num == 0 ? M - 1 : num - 1; return ret; }
    ModInt operator ++ (){ return num = num == M + 1 ? 0 : num + 1; }
    ModInt operator -- (){ return num = num == 0 ? M - 1 : num - 1; }
    // ModInt operator ++ (int){ int ret = num; num = (num + 1) % M; return ret; }
    // ModInt operator -- (int){ int ret = num; num = (num - 1 + M) % M; return ret; }
    // ModInt operator ++ (){ return num = (num + 1) % M; }
    // ModInt operator -- (){ return num = (num - 1 + M) % M; }
    template <class T> ModInt operator += (T n){ num += n; return num = num >= M ? num - M : num; }
    template <class T> ModInt operator -= (T n){ num -= n; return num = num < 0 ? num + M : num; }
    // template <class T> ModInt operator += (T n){ auto ret = num + n; return num = ret >= M ? ret - M : ret; }
    // template <class T> ModInt operator -= (T n){ auto ret = num - n; return num = ret < 0 ? ret + M : ret; }
    // template <class T> ModInt operator += (T n){ return num = (num + n) % M; }
    // template <class T> ModInt operator -= (T n){ return num = (num - n) % M; }
    template <class T> ModInt operator *= (T n){ return num = (ll)num * n % M; }
    template <class T> ModInt operator /= (T n){ return num = (ll)num * modInv(n) % M; }
    template <class T> ModInt operator >>= (T n){ return num = num >> n; }
    template <class T> ModInt operator <<= (T n){ return num = ((ll)num << n) % M; }
    friend ModInt modPow(ModInt base, ModInt ex) {
        ModInt ret = 1;
        while(ex.num){
            if(ex.num & 1){ ret = ret * base; }
            ex >>= 1;
            base = base * base;
        }
        return ret;
    }
    static vector<ModInt> mFacts, mInvFacts;
    friend ModInt modFact(ModInt n){ return mFacts[n.num]; }
    friend ModInt modInvFact(ModInt n){ return mInvFacts[n.num]; }
    friend ModInt modInv(ModInt n){ return modPow(n, M - 2); }
    friend ModInt modC(ModInt n, ModInt k){ return modFact(n) * modInvFact(k) * modInvFact(n - k); }
    friend ModInt modP(ModInt n, ModInt k){ if(n < k){ return 0; } return modFact(n) * modInvFact(n - k); }
    static void init(int n){
        mFacts.resize(n + 1);
        mInvFacts.resize(n + 1);
        mFacts[0] = 1;
        for(int i = 1; i <= n; i++){
            mFacts[i] = mFacts[i - 1] * i;
        }
        mInvFacts[n] = modInv(mFacts[n]);
        for(int i = n - 1; i >= 0; i--){
            mInvFacts[i] = mInvFacts[i + 1] * (i + 1);
        }
    }
    friend istream& operator >> (istream& in, ModInt& e){ return in >> e.num; }
    friend ostream& operator << (ostream& out, const ModInt& e) { return out << e.num; }
};
template <int M>
vector<ModInt<M>> ModInt<M>::mFacts;
template <int M>
vector<ModInt<M>> ModInt<M>::mInvFacts;
// using mint = ModInt<998244353>;
using mint = ModInt<(int)M>;

int n, k;
struct Graph{
    struct Node{
        vector<int> dests;
    };
    vector<Node> nodes;
    Graph(int num): nodes(num){ }
    int id(Node* n){ return n - &nodes[0]; }
    int id(Node& n){ return &n - &nodes[0]; }
    void print(){ for(auto& node : nodes){ prints(id(node), node.dests); } }
    void add1Edge(int from, int dest){
        nodes[from].dests.push_back(dest);
    }
    void add2Edge2(int from, int dest){
        add1Edge(from, dest);
        add1Edge(dest, from);
    }
    mint dfs(int idx, int from = -1){
        if(k < (from == -1 ? 0 : 2)){
            return 0;
        }
        mint ret = modP((mint)k - (from == -1 ? 0 : 2), nodes[idx].dests.size() - 1 + (from == -1 ? 2 : 0));
        printde(k, nodes[idx].dests.size() - 1 + (from == -1 ? 2 : 0), ret);
        for(int didx : nodes[idx].dests){
            if(didx == from){ continue; }
            ret *= dfs(didx, idx);
        }
        return ret;
    }
};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    mint::init(1e6);
    cin >> n >> k;
    Graph g(n);
    // vector<int> es(n);
    for(int i = 0; i < n - 1; i++){
        int a, b;
        cin >> a >> b;
        a--; b--;
        g.add2Edge2(a, b);
        // es[a]++;
        // es[b]++;
    }
    cout << g.dfs(0) << '\n';
    // mint ans = 0;
    // for(int i = 0; i < n; i++){
    //     // ans += modP(k, es[i] - 1);
    // }
}


Measured memory_bytes: 18176