#include <bits/stdc++.h>
using namespace std;
#define repl(i, l, r) for (ll i = (l); i < (r); i++)
#define rep(i, n) repl(i, 0, n)
#define CST(x) cout << fixed << setprecision(x)
using ll = long long;
constexpr ll MOD = 1000000007;
constexpr int inf = 1e9 + 10;
constexpr ll INF = (ll)4e18 + 10;
constexpr int dx[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
constexpr int dy[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
template <class T>
inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T>
inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
int main() {
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(false);

    int n, k;
    cin >> n >> k;
    vector<vector<int>> G(n);
    rep(i, n - 1) {
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    vector<int> s(n);
    vector<vector<ll>> dp(n, vector(n + 1, 0LL));
    auto dfs = [&](auto self, int v, int pre) -> void {
        dp[v][0] = 1;
        for (auto nv : G[v]) {
            if (nv == pre) continue;
            self(self, nv, v);
            vector ndp(n + 1, 0LL);
            rep(i, n) {
                rep(j, n) {
                    if (dp[v][i] and dp[nv][j])
                        ndp[i + j] = (ndp[i + j] + dp[v][i] * dp[nv][j] % MOD) % MOD;
                }
            }
            dp[v] = ndp;
            s[v] += s[nv];
        }
        s[v]++;
        dp[v][s[v]]++;
    };

    dfs(dfs, 0, -1);
    cout << dp[0][k] << endl;
    return 0;
}