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

long dynamic_programming(const unsigned long K, const long now, const long prev, vector<vector<long>>& dp, const vector<vector<long>>& edge){
    auto tapi = [&K](vector<long>& to, const vector<long>& src) -> void{
        size_t N = min(to.size() + src.size() - 1, K + 1);
        vector<long> hoge(N);
        for(int i = 0; i < to.size(); ++i)
            if(to[i])
                for(int j = 0; j < src.size(); ++j){
                    if(i + j > K)break;
                    hoge[i + j] += to[i] * src[j] % 1000000007;
                }
        to = vector<long>(N);
        transform(hoge.begin(), hoge.end(), to.begin(), [](auto i){return i % 1000000007;});
    };
    long ret = 0;
    dp[now][0] = 1;
    for(const auto i : edge[now])
        if(i != prev){
            ret += dynamic_programming(K, i, now, dp, edge);
            tapi(dp[now], dp[i]);
        }
    if(ret + 1 <= K)dp[now].push_back(1);
    return ret + 1;
}

int main(){
    unsigned long N, K;
    cin >> N >> K;

    vector<vector<long>> edge(N);
    for(int i = 1, a, b; i < N; ++i){
        cin >> a >> b;
        edge[a].push_back(b);
        edge[b].push_back(a);
    }

    vector<vector<long>> dp(N, vector<long>(1, 1));
    dynamic_programming(K, 0, 0, dp, edge);
    cout << dp[0][K] << endl;
}