#include <bits/stdc++.h>

#define rep(i, n) for (int (i) = 0; (i) < (int)(n); (i)++)

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;

const int MAXN = 2222;
const ll MOD = 1e9+7;
vector<int> G[MAXN];
ll dp[MAXN][MAXN];

vll dfs(int v, int p) {
    vll ret(1, 1);
    for (int next : G[v]) {
        if (next == p) continue;
        vll tmp = dfs(next, v);
        int n = ret.size();
        int m = tmp.size();
        vll nret(n+m-1);
        for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) {
            (nret[i+j] += ret[i]*tmp[j]) %= MOD;
        }
        ret = nret;
    }
    ret.push_back(1);
    return ret;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, K;
    cin >> N >> K;
    for (int i = 0; i < N-1; i++) {
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }
    cout << dfs(0, -1)[K] << endl;
    return 0;
}