#include<cstdio>
#include<vector>
using namespace std;
const int N=100005;
const int MOD=1000000007;
int aux,n,k,nrf[N];
long long prod;
int main()
{
    freopen("colorare3.in","r",stdin);
    freopen("colorare3.out","w",stdout);
    scanf("%d%d",&n,&k);
    int x,y;
    for(int i=1;i<n;i++)
    {
        scanf("%d%d",&x,&y);
        if(x>y)
        {
            aux=x;
            x=y;
            y=aux;
        }
        nrf[x]++;
    }
    int q=k;
    prod=1;
    for(int i=1;i<=nrf[1];i++)
        prod=((long long)prod*q)%MOD, --q;
    for(int i=2;i<=n;i++)
    {
        q=k-1;
        for(int j=1;j<=nrf[i];j++)
            prod=((long long)prod*q)%MOD, --q;
    }
    printf("%lld",prod);
    return 0;
}