#include <bits/stdc++.h>
using namespace std;
const int P = 1e9 + 7, INF = 0x3f3f3f3f;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long qpow(long long a, long long n) {
  long long r = 1 % P;
  for (a %= P; n; a = a * a % P, n >>= 1)
    if (n & 1) r = r * a % P;
  return r;
}
long long inv(long long first) {
  return first <= 1 ? 1 : inv(P % first) * (P - P / first) % P;
}
inline int rd() {
  int first = 0;
  char p = getchar();
  while (p < '0' || p > '9') p = getchar();
  while (p >= '0' && p <= '9') first = first * 10 + p - '0', p = getchar();
  return first;
}
const int N = 1e6 + 50;
int n, k, sz[N], fa[N];
int Find(int first) { return fa[first] ? fa[first] = Find(fa[first]) : first; }
int main() {
  scanf("%d%d", &n, &k);
  for (int i = 1; i <= n; ++i) sz[i] = 1;
  for (int i = 2; i <= n; ++i) {
    int u, v, w;
    scanf("%d%d%d", &u, &v, &w);
    if (w == 0) {
      u = Find(u), v = Find(v);
      fa[u] = v, sz[v] += sz[u];
    }
  }
  int ans = qpow(n, k);
  for (int i = 1; i <= n; ++i)
    if (Find(i) == i) ans = (ans - qpow(sz[i], k)) % P;
  if (ans < 0) ans += P;
  printf("%d\n", ans);
}
