#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
#define REP(i, n) for(int i=0; i<n; i++)
#define REPi(i, a, b) for(int i=int(a); i<int(b); i++)
#define MEMS(a,b) memset(a,b,sizeof(a))
#define mp make_pair
#define MOD(a, m) ((a % m + m) % m)
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
const ll MOD = 1e9+7;

vector<int> G[2100];

using vec1 = vector<ll>;
using vec2 = vector<vec1>;
using vec3 = vector<vec2>;

vec2 dfs(int v, int p){
    vec2 dp(2, vec1(2));
    dp[0][0] = 1;
    dp[1][1] = 1;
    for(auto& nv : G[v]){
        if(nv == p) continue;
        auto ndp = dfs(nv, v);

        int sz_v = dp.size();
        int sz_nv = ndp.size();
        vec2 dp_v(sz_v + sz_nv, vec1(2));
        swap(dp_v, dp);

        REP(k0, sz_v){
            REP(k1, sz_nv){
                REP(j0, 2){
                    REP(j1, 2){
                        if(dp_v[k0][j0] == 0) continue;
                        if(ndp[k1][j1] == 0) continue;
                        auto val = (dp_v[k0][j0] * ndp[k1][j1]) % MOD;
                        int ni = k0+k1;
                        int nj = -1;
                        //if(j0 == 1 && j1 == 1) nj = 1;
                        //else nj = 0;
                        if(j0 == 1){
                            if(j1 == 1) nj = 1;
                            else continue;
                        } else nj = 0;
                        dp[ni][nj] += val;
                        dp[ni][nj] %= MOD;
                    }
                }
            }
        }
    }

    return dp;
}

int main(){
    int N, K;
    cin >> N >> K;
    REP(i,N-1){
        int a, b;
        cin >> a >> b;
        G[a].push_back(b);
        G[b].push_back(a);
    }

    auto dp = dfs(0, -1);
    ll ans = dp[K][0] + dp[K][1];
    cout << ans % MOD << endl;

    return 0;
}