/* -*- coding: utf-8 -*-
 *
 * 196.cc: No.196 典型DP (1) - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 2000;

typedef long long ll;
const ll MOD = 1000000007;

/* typedef */

typedef vector<int> vi;

/* global variables */

int n, k;
int prts[MAX_N], ncs[MAX_N];
vi nbrs[MAX_N], clds[MAX_N];
ll dp[MAX_N][MAX_N + 1], udp[2][MAX_N + 1];

/* subroutines */

void make_tree(int u, int pu = -1) {
  prts[u] = pu;
  ncs[u] = 1;
  vi &nbru = nbrs[u];
  for (vi::iterator vit = nbru.begin(); vit != nbru.end(); vit++) {
    int &v = *vit;
    if (v != pu) {
      clds[u].push_back(v);
      make_tree(v, u);
      ncs[u] += ncs[v];
    }
  }
}

void rec(int u) {
  int usize = sizeof(ll) * (ncs[u] + 1);
  memset(udp[0], 0, usize);
  udp[0][0] = 1;
  int cur = 0, nxt = 1;

  int sumnc = 0;
  vi &cldu = clds[u];
  for (vi::iterator vit = cldu.begin(); vit != cldu.end(); vit++)
    rec(*vit);

  for (vi::iterator vit = cldu.begin(); vit != cldu.end(); vit++) {
    int &v = *vit;

    //printf("u=%d: sumnc=%d, ncs[%d]=%d\n", u, sumnc, v, ncs[v]);
    //for (int j = 0; j <= sumnc; j++) printf(" %lld", udp[cur][j]);
    //putchar('\n');
    //for (int j = 0; j <= ncs[v]; j++) printf(" %lld", dp[v][j]);
    //putchar('\n');

    memset(udp[nxt], 0, usize);
    for (int i = sumnc; i >= 0; i--)
      for (int j = ncs[v]; j >= 0; j--)
	udp[nxt][i + j] =
	  (udp[nxt][i + j] + udp[cur][i] * dp[v][j] % MOD) % MOD;

    sumnc += ncs[v];
    cur ^= 1, nxt ^= 1;
  }

  udp[cur][ncs[u]] = 1;
  memcpy(dp[u], udp[cur], usize);
}

/* main */

int main() {
  cin >> n >> k;

  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    nbrs[a].push_back(b);
    nbrs[b].push_back(a);
  }

  make_tree(0);
  //for (int i = 0; i < n; i++) printf("%d ", ncs[i]); putchar('\n');

  rec(0);
  printf("%lld\n", dp[0][k]);

  for (int i = 0; false && i < n; i++) {
    printf("%d:", i);
    for (int j = 0; j <= n; j++) printf(" %lld", dp[i][j]);
    putchar('\n');
  }
  return 0;
}