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

const long long int mod = 1000000007;
vector<vector<long long int>> g(100005);

// bin_expo(int a, int b) calculates a*a*a*a ......... *a (b times)
long long int bin_expo(int a,int b){
    if(b==0)return 1;
    long long int res = bin_expo(a,b/2);
    if(b%2){
        return (((res*res)%mod)*a)%mod;
    }
    else{
        return (res*res)%mod;
    }
}

void dfs(int src,vector<bool> &visited,int *count){
    (*count)++;
    visited[src] = true;

    for(auto i : g[src]){
        if(!visited[i]){
            dfs(i,visited,count);
        }
    }
}

int totalMagicalSequence(int N, int X, vector<vector<int>> &edge){
    long long int tot = bin_expo(N, X);

    for(int i=0;i<N-1;i++){
        if(edge[i][2]==0){
            g[edge[i][0]].push_back(edge[i][1]);
            g[edge[i][1]].push_back(edge[i][0]);
        }
    }

    vector<bool> visited(N+1,false);

    for(int i=1;i<=N;i++){
        if(!visited[i]){
            int count =0;
            dfs(i,visited,&count);
            tot = (tot - bin_expo(count,X) + mod) %mod;
        }
    }
    return tot;
}

signed main() {
    int N,X;
    cin>>N>>X;

    vector<vector<int>> edge(N-1);
    for(int i=0;i<N-1;i++){
        for(int j=0;j<3;j++){
            int x;
            cin>>x;
            edge[i].push_back(x);
        }
    }

    cout<<totalMagicalSequence(N,X,edge)<<endl;
}