#include <bits/stdc++.h>

using namespace std;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
template<class T> inline T sqr(T x) {return x*x;}

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a)  (a).begin(),(a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define exist(s,e) ((s).find(e)!=(s).end())
#define range(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)  range(i,0,n)
#define clr(a,b) memset((a), (b) ,sizeof(a))
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi  = acos(-1.0);
const ll INF =1LL << 62;
const int inf =1 << 29;

const ll mod= 1000000007;
const int nmax=2010;

vi graph[nmax];
int num[nmax];
ll dp[nmax][nmax];
ll dp2[nmax];


void dfs(int v,int p){
	for(auto &v2:graph[v]) if(v2!=p) dfs(v2,v);
	rep(i,nmax) dp[v][i]=0;
	dp[v][0]=1LL,num[v]=0;
	for(auto &v2:graph[v])if(v2!=p) {
		rep(i,nmax) dp2[i]=0;
		rep(i,num[v]+1)rep(j,num[v2]+1)
			dp2[i+j]=(dp2[i+j]+dp[v][i]*dp[v2][j])%mod;
		rep(i,nmax) dp[v][i]=dp2[i];
		num[v]+=num[v2];
	}
	num[v]++,dp[v][num[v]]=1LL;
	return;
}


int main(void){
	int N,K;
	cin >> N >> K;
	rep(i,N-1){
		int a,b;
		cin >> a >> b;
		graph[a].pb(b);
		graph[b].pb(a);
	}
	dfs(0,-1);
	cout << dp[0][K] << endl;
	return 0;
}