#include<bits/stdc++.h>
#define rep(i,n,m) for(int i = (n); i <(m); i++)
#define rrep(i,n,m) for(int i = (n) - 1; i >=(m); i--)
using namespace std;
using ll = long long;
const int MAX_N = 2002;
const ll MOD = 1000000007;

vector<int> graph[MAX_N];
ll dp[MAX_N][MAX_N];
int num[MAX_N];
int k;

void dfs(int root, int par)
{

    dp[root][0] = 1;
    // dp[root][1] = 1;
    num[root] = 1;
    for (auto ch: graph[root])
    if (ch != par)
    {
        dfs(ch, root);

        vector<int> dp_now(MAX_N, 0);
        rep(i, 0, num[ch]+1)
        {
            rep(j, 0, num[root]+1)
            {
                if (i+j > k) break;
                dp_now[i+j] += dp[root][j] * dp[ch][i];
                dp_now[i+j] %= MOD;
                // cout << root << ' ' << i << ' ' << j << " : "<< dp[root][j] << ' ' << dp[ch][i] << endl;
            }
        }
        
        num[root] += num[ch];
        rep(i, 0, MAX_N) dp[root][i] = dp_now[i];
    }
    dp[root][num[root]] = 1;
    // cout << root << ' ' << dp[root][0] << ' ' << dp[root][1] << endl;
}

int main()
{
    int n;
    cin >> n >> k;

    rep(i, 0, n-1)
    {
        int a, b;
        cin >> a >> b;
        // --a, --b;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    dfs(0, -1);
    cout << dp[0][k] << endl;
    return 0;
}