#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
vector<int> adj[105];
int n, k, dp[105][50], tmp[50];
void dfs(int u, int p) {
  dp[u][0] = dp[u][k + 1] = 1;
  for (int x = 0; x < adj[u].size(); x++) {
    int v = adj[u][x];
    if (v == p) continue;
    dfs(v, u);
    memset(tmp, 0, sizeof tmp);
    for (int i = 0; i <= 2 * k; i++) {
      for (int j = 0; j <= 2 * k; j++) {
        if (i + j <= 2 * k)
          tmp[min(i, j + 1)] =
              (tmp[min(i, j + 1)] + 1ll * dp[u][i] * dp[v][j]) % mod;
        else
          tmp[max(i, j + 1)] =
              (tmp[max(i, j + 1)] + 1ll * dp[u][i] * dp[v][j]) % mod;
      }
    }
    for (int i = 0; i <= 2 * k; i++) dp[u][i] = tmp[i];
  }
}
int main() {
  scanf("%d %d", &n, &k);
  int i, ans = 0;
  for (i = 1; i < n; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  dfs(1, 0);
  for (i = 0; i <= k; i++) ans = (ans + dp[1][i]) % mod;
  printf("%d\n", ans);
  return 0;
}
