// #pragma GCC optimize ("Ofast")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC target ("avx,avx2,fma")
#include <bits/stdc++.h>

#define rep(i, a, b) for(int i = (a); i <= (b); i ++)
using std::cin, std::cout, std::cerr;
using ll = long long;

const int P = 1e9 + 7;

const int N = 2000 + 1;
ll f[N][N];
int sz[N];
std::vector<int> e[N];

int main() {
    std::ios::sync_with_stdio(false);
    int n, k; cin >> n >> k;
    rep(i, 1, n - 1) {
        int u, v; cin >> u >> v;
        e[u].push_back(v);
        e[v].push_back(u);
    }

    std::function<void(int, int)> dfs = [&](int x, int p) {
        sz[x] = 1;
        f[x][0] = f[x][1] = 1;
        for(int i : e[x]) if(i != p) {
            dfs(i, x);
            for(int j = sz[x] + sz[i]; j >= 1; j --)
                for(int k = 1; k <= sz[i]; k ++)
                    if(j >= k + 1) {
                        f[x][j] += f[x][j - k] * f[i][k];
                        f[x][j] %= P;
                    }
            sz[x] += sz[i];
        }
    };
    dfs(0, -1);
    cout << f[0][n - k] << '\n';
}