#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 5, mod = 1e9 + 7;
template <class o>
inline void qr(o &x) {
  x = 0;
  char c = getchar();
  int f = 1;
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = x * 10 + (c ^ 48);
    c = getchar();
  }
  x *= f;
}
template <class o>
void qw(o x) {
  if (x / 10) qw(x / 10);
  putchar(x % 10 + 48);
}
template <class o>
void pr1(o x) {
  if (x < 0) putchar('-'), x = -x;
  qw(x);
  putchar(' ');
}
template <class o>
void pr2(o x) {
  if (x < 0) putchar('-'), x = -x;
  qw(x);
  puts("");
}
inline int ksm(int a, int b = mod - 2) {
  int ans = 1;
  for (; b; b >>= 1, a = 1ll * a * a % mod)
    if (b & 1) ans = 1ll * ans * a % mod;
  return ans;
}
inline int add(int a, int b) { return a += b, a >= mod ? a - mod : a; }
inline int sub(int a, int b) { return a -= b, a < 0 ? a + mod : a; }
vector<pair<int, int> > e[N];
int siz[N], col[N], cnt, pw[N];
void dfs(int x) {
  ++siz[cnt];
  col[x] = cnt;
  for (pair<int, int> t : e[x]) {
    int y = t.first, z = t.second;
    if (z || col[y]) continue;
    dfs(y);
  }
}
void solve() {
  int n, k;
  qr(n), qr(k);
  for (int i = 1; i <= n; ++i) pw[i] = ksm(i, k);
  for (int i = 1; i < n; ++i) {
    int x, y, z;
    qr(x), qr(y), qr(z);
    e[x].emplace_back(y, z);
    e[y].emplace_back(x, z);
  }
  int ans = pw[n];
  for (int i = 1; i <= n; ++i)
    if (!col[i]) {
      ++cnt;
      dfs(i);
      ans = sub(ans, pw[siz[cnt]]);
    }
  pr2(ans);
}
int main() {
  solve();
  return 0;
}
