#include <bits/stdc++.h>
using namespace std;
ostream& operator<<(ostream& os, const vector<int>& a) {
  for (auto x : a) os << x << ' ';
  os << '\n';
  return os;
}
const int Mod = 1e9 + 7;
int n, K;
int S[205][205];
vector<int> G[100005];
void inc(int& x) {
  if (x >= Mod) x -= Mod;
}
void dec(int& x) {
  if (x < 0) x += Mod;
}
vector<int> operator+(vector<int> a, vector<int> b) {
  if (a.size() < b.size()) a.resize(b.size());
  for (int i = (signed)b.size() - 1; ~i; i--) inc(a[i] += b[i]);
  return a;
}
vector<int> operator*(vector<int> a, vector<int> b) {
  int n = (signed)a.size(), m = (signed)b.size();
  vector<int> c(min(n + m - 1, K + 1), 0);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m && i + j <= K; j++) {
      c[i + j] = (c[i + j] + 1ll * a[i] * b[j]) % Mod;
    }
  }
  return c;
}
typedef class dp_t {
 public:
  vector<int> f, g;
  dp_t(int p, int fa) {
    for (auto e : G[p]) {
      if (e ^ fa) {
        dp_t t(e, p);
        f = (f + g) * (t.f + t.g) + t.f + f;
        g = g + t.g;
      }
    }
    f = f * vector<int>{2} + g + vector<int>{1};
    if (fa) g = g * vector<int>{1, 1} + f * vector<int>{0, 1};
  }
} dp_t;
int main() {
  scanf("%d%d", &n, &K);
  for (int i = 1, u, v; i < n; i++) {
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  S[0][0] = 1;
  for (int i = 1; i <= K; i++) {
    S[i][0] = 0, S[i][i] = 1;
    for (int j = 1; j < i; j++) {
      S[i][j] = (1ll * S[i - 1][j] * j + S[i - 1][j - 1]) % Mod;
    }
  }
  dp_t d(1, 0);
  int fac = 1, ans = 0;
  for (int i = 0; i <= K && i < (signed)d.f.size(); i++) {
    ans = (ans + 1ll * S[K][i] * fac % Mod * d.f[i]) % Mod;
    fac = 1ll * fac * (i + 1) % Mod;
  }
  printf("%d\n", ans);
  return 0;
}
