#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll MOD = 1e9 + 7;

vector<vector<int>> G;

void dfs(int idx, int par, vector<ll>& V) {
    V.emplace_back(1);
    for (auto& nxt : G[idx]) {
        if (nxt == par)
            continue;
        int N = V.size();
        vector<ll> V_nxt, V_memo = V;
        dfs(nxt, idx, V_nxt);
        V.resize(V.size() + V_nxt.size() - 1);
        for (int i = 1; i < V_nxt.size(); i++) {
            for (int j = 0; j < N; j++) {
                (V[j + i] += V_memo[j] * V_nxt[i]) %= MOD;
            }
        }
    }
    V.emplace_back(1);
}

int main() {
    int N, K;
    cin >> N >> K;
    G.resize(N);
    for (int i = 0; i < N - 1; i++) {
        int a, b;
        cin >> a >> b;
        G[a].emplace_back(b);
        G[b].emplace_back(a);
    }

    vector<ll> V;
    dfs(0, -1, V);
    cout << V[K] << endl;
}