#include<bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    int n, k;
    cin >> n >> k;
    vector<vector<int>> g(n);
    vector<vector<ll>> dp(n + 1);
    for(int i = 1, u, v; i < n; i++){
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    function<void(int,int)> dfs = [&](int v, int p){
        dp[v].resize(1, 1);
        for(auto &&u:g[v]){
            if(u == p)continue;
            dfs(u, v);
            vector<ll> ndp(dp[v].size() + dp[u].size() - 1);
            for(int j = 0; j < dp[v].size(); j++){
                for(int k = 0; k < dp[u].size(); k++){
                    (ndp[j + k] += dp[v][j] * dp[u][k]) %= 1000000007;
                }
            }
            swap(dp[v], ndp);
        }
        dp[v].push_back(1);
    };
    dfs(0, -1);
    cout << dp[0][k] << endl;
}