#include <iostream>
#include <stdio.h>
#include <fstream>
#include <algorithm>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <limits.h>
#include <math.h>
#include <functional>
#include <bitset>
#include <iomanip>
#include <cassert>

#define repeat(i,n) for (long long i = 0; (i) < (n); ++ (i))
#define debug(x) cerr << #x << ": " << x << '\n'
#define debugArray(x,n) for(long long i = 0; (i) < (n); ++ (i)) cerr << #x << "[" << i << "]: " << x[i] << '\n'
#define debugArrayP(x,n) for(long long i = 0; (i) < (n); ++ (i)) cerr << #x << "[" << i << "]: " << x[i].first<< " " << x[i].second << '\n'

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> Pii;
typedef vector<int> vint;
typedef vector<ll> vll;
const ll INF = INT_MAX;
const ll MOD = 1e9+7;

int N,K;
vector<vint> G;
ll dp[2010][2010];
ll tmp[2010];
ll size[2010];

void dfs(int v,int par){
  size[v]=1;
  dp[v][0]=1;
  for(int chi:G[v])if(chi!=par){
    dfs(chi,v);
    size[v]+=size[chi];
    fill(tmp,tmp+K+1,0);
    for(int k=K;k>=0;k--){
      repeat(l,k+1){
        tmp[k] = (tmp[k]+dp[v][k-l]*dp[chi][l]%MOD)%MOD;
      }
    }
    swap(tmp,dp[v]);
  }
  if(size[v]<=K){
    dp[v][size[v]]=1;
  }
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin>>N>>K;
  G.resize(N);
  repeat(i,N-1){
    int a,b;cin>>a>>b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  dfs(0,-1);
  //debug(dp[3][1]);
  cout << dp[0][K] << endl;
  return 0;
}