#include <bits/stdc++.h>
using namespace std;

const int MOD = 1e9 + 7;

int n, m;
int gr[100005];
int main()
{
    freopen("colorare3.in", "r", stdin);
    freopen("colorare3.out", "w", stdout);

    scanf("%d%d", &n, &m);
    int x, y;
    for(int i = 1; i < n ; ++i){
        scanf("%d%d", &x, &y);
        ++gr[x]; ++gr[y];
    }

    int Sol = 1;
    for(int i = 0; i < gr[1] ; ++i) Sol = (1LL * Sol * (m - i)) % MOD;

    for(int i = 2; i <= n ; ++i){
        for(int j = 1; j < gr[i] ; ++j)
            Sol = (1LL * Sol * (m - j)) % MOD;
    }

    printf("%d", Sol);
    return 0;
}