#include <bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define pb push_back
#define rep(i, s, n) for (int i = s; i < n; i++)
#define rrep(i, s, n) for (int i = (n)-1; i >= (s); i--)
#define all(a) a.begin(),a.end()
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
const long long MOD = 1000000007, INF = 1e18;
template<class T>inline bool chmax(T& a,T b){if(a<b){a=b;return true;}return false;}
template<class T>inline bool chmin(T& a,T b){if(a>b){a=b;return true;}return false;}
string get_str(string s) {
	s+=',';
	string ret="";
	for(int i=0; i<s.size(); i++) {
		if(s[i]==',') ret+="=%ld, ";
		else ret+=s[i];
	}
	return ret;
}
#define dump(...) printf(get_str(#__VA_ARGS__).c_str(),__VA_ARGS__);cout<<endl
 
#define endl '\n'
#define IOS()                     \
	ios_base::sync_with_stdio(0); \
	cin.tie(0)
 
//******************************************************************************
template<typename T>vector<T>
make_v(size_t a){return vector<T>(a);}
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
	return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}
 
template<typename T,typename V>
typename enable_if<is_class<T>::value==0>::type
fill_v(T &t,const V &v){t=v;}
 
template<typename T,typename V>
typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t,const V &v){
	for(auto &e:t) fill_v(e,v);
}

int N,K;
vint g[2002];

vector<int>dfs(int now,int par){
	vector<int>dp(1,1);
	for(auto e:g[now]){
		if(e==par)continue;
		vector<int>tmp = dfs(e,now);
		vector<int>new_dp(dp.size()+tmp.size()-1);
		rep(i,0,dp.size()){
			rep(j,0,tmp.size()){
				(new_dp[i+j]+=dp[i]*tmp[j])%=MOD;
			}
		}
		dp=new_dp;
	}
	dp.push_back(1);
	return dp;
}


signed main()
{
	IOS();
	cin>>N>>K;
	rep(i,0,N-1){
		int a,b;
		cin>>a>>b;
		g[a].push_back(b);
		g[b].push_back(a);
	}
	cout<<dfs(0,-1)[K]<<endl;
}