#include <iostream>
#include <vector>
#include <functional>
#define repeat(i,n) for (int i = 0; (i) < int(n); ++(i))
using ll = long long;
using namespace std;
template <typename X, typename T> auto vectors(X x, T a) { return vector<T>(x, a); }
template <typename X, typename Y, typename Z, typename... Zs> auto vectors(X x, Y y, Z z, Zs... zs) { auto cont = vectors(y, z, zs...); return vector<decltype(cont)>(x, cont); }
const int mod = 1e9+7;
void merge(vector<int> const & a, vector<int> const & b, vector<int> & c, int size) {
    int n = c.size();
    repeat (i,n) {
        ll acc = 0;
        if (i < size) {
            repeat (j,i+1) {
                int k = i - j;
                acc += a[j] *(ll) b[k] % mod;
            }
            acc %= mod;
        }
        c[i] = acc;
    }
}
int main() {
    int n, k; cin >> n >> k;
    vector<vector<int> > g(n);
    repeat (i,n-1) {
        int a, b; cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    vector<vector<int> > dp = vectors(n, n+1, int());
    vector<int> size(n);
    vector<int> acc(n+1);
    function<void (int, int)> go = [&](int i, int parent) {
        size[i] = 1;
        dp[i][0] = 1;
        for (int j : g[i]) if (j != parent) {
            go(j, i);
            size[i] += size[j];
            merge(dp[i], dp[j], acc, size[i]);
            dp[i].swap(acc);
        }
        dp[i][size[i]] = 1;
    };
    go(0, -1);
    cout << dp[0][k] << endl;
    return 0;
}