#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
using Graph = vector< vector<int> >;

const long long int MOD = 1000000007LL;
int N, K, num[2010];

void dfs(Graph &G, int cur, int par=-1) {
    num[cur] = 1;
    for(auto to : G[cur]) {
        if(to == par) continue;
        dfs(G, to, cur);
        num[cur] += num[to];
    }
}

vector<long long int> solve(Graph &G, int cur, int par=-1) {
    // 全く塗らない、全部塗る
    vector<long long int> dp(N, 0);
    dp[0] = dp[ num[cur] ] = 1;

    int sum = 0;
    for(auto to : G[cur]) {
        if(to == par) continue;
        // cur は塗らない
        vector<long long int> child = solve(G, to, cur);

        for(int k=sum; k>=0; k--) {
            for(int pt=num[to]; pt>=1; pt--) {
                (dp[k+pt] += dp[k] * child[pt]) %= MOD;
            }
        }
        sum += num[to];
    }
    return dp;
}

int main() {
    scanf("%d%d", &N, &K);

    Graph G(N);
    for(int i=0; i<N-1; i++) {
        int u, v; scanf("%d%d", &u, &v);
        G[u].push_back(v);
        G[v].push_back(u);
    }

    dfs(G, 0);
    vector<long long int> ans = solve(G, 0);

    printf("%lld\n", ans[K]);
    return 0;
}