#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;
vector<int> merge(vector<int> & a, vector<int> & b) {
    int n = a.size() + b.size() + 3;
    vector<int> c(n);
    repeat (i, a.size()) {
        repeat (j, b.size()) {
            c[i + j] += a[i] *(ll) b[j] % mod;
            c[i + j] %= mod;
        }
    }
    while (not c.empty() and c.back() == 0) c.pop_back();
    return c;
}
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(n);
    vector<int> size(n);
    function<void (int, int)> go = [&](int i, int parent) {
        size[i] = 1;
        if (dp[i].size() <= 0) dp[i].resize(1);
        dp[i][0] = 1;
        for (int j : g[i]) if (j != parent) {
            go(j, i);
            dp[i] = merge(dp[i], dp[j]);
            size[i] += size[j];
        }
        if (dp[i].size() <= size[i]) dp[i].resize(size[i] + 1);
        dp[i][size[i]] = 1;
    };
    go(0, -1);
    cout << dp[0][k] << endl;
    return 0;
}