#include <bits/stdc++.h>
#define rep(i, n) for (lli i = 0; i < (n); i++)
#define rrep(i, n) for (lli i = (n)-1; i >= 0; i--)
using namespace std;
using lli = long long int;
lli mod = 1e9 + 7;
vector<int> e[2005];
lli dp[2005][2005] = {};
lli memo[2005] = {};

int n, k;
// iの部分木でj個色が塗られている場合の数
int dfs(int cur, int par)
{
    if (cur != 0 and e[cur].size() == 1) {
        // leaf
        dp[cur][1] = 1;
        dp[cur][0] = 1;
        memo[cur] = 1;
        return 1;
    }
    int size = 1;
    for (auto s : e[cur]) {
        if (s == par)
            continue;
        size += dfs(s, cur);
    }
    dp[cur][0] = 1;
    for (auto s : e[cur]) {
        if (s == par)
            continue;
        vector<lli> tmp(n + 1, 0);

        rep(i, n + 1)
        {
            tmp[i] = dp[cur][i];
        }
        vector<lli> hoge(n + 1, 0);
        rep(i, memo[s] + 1)
        {
            rep(j, n + 1)
            {
                if (i + j > n)
                    continue;
                hoge[i + j] += (tmp[j] % mod * dp[s][i]) % mod;
                hoge[i + j] %= mod;
            }
        }

        rep(i, n + 1) dp[cur][i] = hoge[i];
    }
    dp[cur][size] = 1;
    memo[cur] = size;
    return size;
}
int main()
{
    cin >> n >> k;
    int a, b;
    rep(i, n - 1)
    {
        cin >> a >> b;
        e[a].push_back(b);
        e[b].push_back(a);
    }
    dfs(0, -1);

    cout << dp[0][k] << endl;
}