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

using Graph = vector<vector<int>>;

const int MOD = 1000000007;
int N, K;
Graph G;
vector<vector<long long>> dp;

void dfs(int v, int pv) {
    dp[v].resize(1, 1);
    for (int nv : G[v]) if (nv != pv) {
        dfs(nv, v);
        vector<long long> merged(dp[v].size() + dp[nv].size() - 1);
        for (int i = 0; i < dp[v].size(); ++i) for (int j = 0; j < dp[nv].size(); ++j) {
            (merged[i + j] += dp[v][i] * dp[nv][j]) %= MOD;
        }
        dp[v] = merged;
    }
    dp[v].push_back(1);
}

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