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

using int64 = long long;

const int64 MOD = 1e9 + 7;

vector<int> T[2010];

int64 dp[2010][2010][2];
int size[2010];

int N, K;

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

    dp[v][0][0] = dp[v][1][1] = 1;

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

        int values[2010][2] = {};

        for (int k = size[v]; k >= 0; k--) {
            for (int st = 0; st <= 1; st++) {
                if (k == 0 and st == 1) continue;

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

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;

    for (int st = 0; st <= 1; st++) {
        cerr << "st: " << st << " dp: " << dp[0][K][st] << endl;
    }
    
    return 0;
}