#include <cstdio>
#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <cmath>
#include <iomanip>
#include <cassert>
#include <bitset>
using namespace std;

typedef pair<int, int> P;
#define rep(i, n) for (int i=0; i<(n); i++)
#define all(c) (c).begin(), (c).end()
#define uniq(c) c.erase(unique(all(c)), (c).end())
#define index(xs, x) (int)(lower_bound(all(xs), x) - xs.begin())
#define _1 first
#define _2 second
#define pb push_back
#define INF 1145141919
#define MOD 1000000007
inline void add(int &x, int v) {
  x += v;
  if (x >= MOD) x -= MOD;
}

int N, K;
vector<int> G[2000];

int sz[2000];
int dfs(int x, int p) {
  sz[x] = 1;
  for (int t : G[x]) {
    if (t == p) continue;
    sz[x] += dfs(t, x);
  }
  return sz[x];
}

int dp[2000][2001];
int dp2[2][2001];
void f(int x, int p) {
  for (int t : G[x]) {
    if (t == p) continue;
    f(t, x);
  }

  int n = sz[x];
  rep(i, N+1) dp2[0][i] = 0;
  dp2[0][0] = 1;

  for (int t : G[x]) {
    if (t == p) continue;
    rep(i, n+1) dp2[1][i] = 0;
    for (int j=n; j>=0;j--){
      if (dp2[0][j] == 0) continue;
      rep(k, sz[t]+1) {
        if (j+k > n) break;
        add(dp2[1][j+k], (1LL*dp[t][k]*dp2[0][j])%MOD);
      }
    }
    swap(dp2[0], dp2[1]);
  }
  assert(dp2[0][n] == 0);
  dp2[0][n] = 1;
  rep(i, n+1) dp[x][i] = dp2[0][i];
}

signed main() {
  ios::sync_with_stdio(false); cin.tie(0);
  cin >> N >> K;
  rep(i, N-1) {
    int a, b;
    cin >> a >> b;
    G[a].pb(b);
    G[b].pb(a);
  }
  dfs(0, -1);
  f(0, -1);
  cout << dp[0][K] << "\n";
  return 0;
}