#include <bits/stdc++.h>
using i64 = long long;
template <class T>
T pow(T x, T n, T mod) {
  T ret = 1;
  while (n > 0) {
    if ((n & 1) == 1) ret = (ret * x) % mod;
    x = (x * x) % mod;
    n >>= 1;
  }
  return ret;
}
template <class T>
T inverse(T x, T p) {
  return pow(x, p - 2, p);
}
template <class T = int>
class UF {
  T *par;

 public:
  UF(T n) : par(new T[n]) {
    for (T i = 0; i < n; i++) par[i] = i;
  }
  ~UF() { delete[] par; }
  T root(T x) {
    if (par[x] == x) return x;
    return par[x] = root(par[x]);
  }
  bool same(T x, T y) { return root(x) == root(y); }
  void unite(T x, T y) {
    x = root(x);
    y = root(y);
    if (x != y) par[x] = y;
  }
};
constexpr i64 mod = 1000000007;
std::vector<std::deque<std::pair<int, int>>> g;
int main() {
  i64 n, k;
  scanf("%lld%lld", &n, &k);
  g.resize(n);
  UF<> uft(n);
  std::vector<int> s(n, 1);
  for (int i = 1; i < n; i++) {
    int u, v, x;
    scanf("%d%d%d", &u, &v, &x);
    u--;
    v--;
    g[u].emplace_back(v, x);
    g[v].emplace_back(u, x);
    if (!x) {
      uft.unite(u, v);
    }
  }
  std::map<int, std::deque<int>> m;
  for (int i = 0; i < n; i++) {
    m[uft.root(i)].push_back(i);
  }
  i64 ret = 0;
  for (auto &el : m) {
    i64 size = el.second.size();
    ret = (ret + pow(size, k, mod)) % mod;
  }
  ret = (pow(n, k, mod) + mod - ret) % mod;
  std::cout << ret << std::endl;
  return 0;
}
