#include <iostream>
#include <vector>
using namespace std;

using int64 = long long;

const int64 MOD = 1e9 + 7;

vector<int> T[2010];

int64 dp[2010][2010];
int size[2010];

int N, K;

int64 dfs(int v, int par) {
    size[v] = 1;

    dp[v][0] = 1;

    for (int to : T[v]) {
        if (to == par) continue;
        dfs(to, v);

        int64 values[2010] = {};

        for (int k = min(K, size[v] - 1); k >= 0; k--) {
            for (int subk = 0; subk + k <= min(size[v] + size[to] - 1, K) and subk <= size[to]; subk++) {
                (values[k + subk] += dp[v][k] * dp[to][subk]) %= MOD;
            }
        }
        // valuesをdpに移す
        size[v] += size[to];
        for (int k = 0; k <= min(K, size[v]); k++) for (int st = 0; st <= 1; st++) dp[v][k] = values[k];
    }
    dp[v][size[v]] = 1;
    return dp[v][K];
}

int main() {
    cin >> N >> K;

    for (int i = 0; i < N - 1; i++) {
        int a, b;
        cin >> a >> b;

        T[a].push_back(b);
        T[b].push_back(a);
    }

    cout << dfs(0, -1) << endl;
    
    return 0;
}