#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;

typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> P;
typedef pair<int,int> Pi;
#define rep(i,n) for(ll i=0;i<n;i++)
#define FOR(i,a,b) for(ll i=a;i<b;i++)
#define rrep(i,n) for(ll i=n-1;i>=0;i--)
#define rFOR(i,a,b) for(ll i=a-1;i>=b;i--)
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define endl "\n"

istream &operator>>(istream &is, modint &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint &a) { return os << a.val(); }
istream &operator>>(istream &is, modint998244353 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint998244353 &a) { return os << a.val(); }
istream &operator>>(istream &is, modint1000000007 &a) { long long v; is >> v; a = v; return is; }
ostream &operator<<(ostream &os, const modint1000000007 &a) { return os << a.val(); }

template<typename T> inline bool chmax(T &a, T b){if(a<b){a=b;return true;}return false;}
template<typename T> inline bool chmin(T &a, T b){if(a>b){a=b;return true;}return false;}
template<typename T> ostream& operator<<(ostream& s,const complex<T>& d) {return s<<"("<<d.real()<<", "<<d.imag()<< ")";}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const pair<T1,T2>& d) {return s<<"("<<d.first<<", "<<d.second<<")";}
template<typename T> ostream& operator<<(ostream& s, const vector<T>& d){int len=d.size();rep(i,len){s<<d[i];if(i<len-1) s<<" ";}return s;}
template<typename T> ostream& operator<<(ostream& s,const vector<vector<T>>& d){int len=d.size();rep(i,len){s<<d[i]<<endl;}return s;}
template<typename T> ostream& operator<<(ostream& s,const set<T>& v){s<<"{ ";for(auto itr=v.begin();itr!=v.end();++itr) {if (itr!=v.begin()) {s<< ", ";}s<<(*itr);}s<<" }";return s;}
template<typename T> ostream& operator<<(ostream& s,const multiset<T>& v){s<<"{ ";for(auto itr=v.begin();itr!=v.end();++itr) {if (itr!=v.begin()) {s<< ", ";}s<<(*itr);}s<<" }";return s;}
template<typename T1, typename T2> ostream& operator<<(ostream& s,const map<T1,T2>& m){s<<"{"<<endl;for(auto itr=m.begin();itr!=m.end();++itr){s<<" "<<(*itr).first<<" : "<<(*itr).second<<endl;}s<<"}"<<endl;return s;}
template<class T> vector<T> make_vec(size_t n, T a) { return vector<T>(n, a); }
template<class... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec(ts...))>(n, make_vec(ts...)); }

const ll mod=1'000'000'007;
const ll inf=1'000'000'000'000'000'00;
const int INF=1'000'000'000;
const double EPS=1e-10;
const double PI=acos(-1);

using mint=modint1000000007;

int main(){
    cin.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);
    }
    auto dp=make_vec(n,n+1,2,mint(0));
    auto sz=make_vec(n,0);
    auto dfs=[&](auto &&dfs,int v,int pre)->void{
        sz[v]=1;
        dp[v][1][1]=1;
        dp[v][0][0]=1;
        for(auto &&to:g[v]){
            if(to==pre) continue;
            dfs(dfs,to,v);
            int x=sz[v],y=sz[to];
            auto ndp=make_vec(x+y+1,2,mint(0));
            rep(i,x+1)rep(j,y+1){
                ndp[i+j][0]+=dp[v][i][0]*dp[to][j][0];
                ndp[i+j][0]+=dp[v][i][0]*dp[to][j][1];
                ndp[i+j][1]+=dp[v][i][1]*dp[to][j][1];
            }
            sz[v]+=sz[to];
            dp[v]=ndp;
        }
    };
    dfs(dfs,0,-1);
    cout<<dp[0][k][0]+dp[0][k][1]<<endl;
}