#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

template<int MOD>
struct ModInt {
	static const int Mod = MOD;
	unsigned x;
	ModInt(): x(0) { }
	ModInt(signed sig) { int sigt = sig % MOD; if(sigt < 0) sigt += MOD; x = sigt; }
	ModInt(signed long long sig) { int sigt = sig % MOD; if(sigt < 0) sigt += MOD; x = sigt; }
	int get() const { return (int)x; }
	
	ModInt &operator+=(ModInt that) { if((x += that.x) >= MOD) x -= MOD; return *this; }
	ModInt &operator-=(ModInt that) { if((x += MOD - that.x) >= MOD) x -= MOD; return *this; }
	ModInt &operator*=(ModInt that) { x = (unsigned long long)x * that.x % MOD; return *this; }
	
	ModInt operator+(ModInt that) const { return ModInt(*this) += that; }
	ModInt operator-(ModInt that) const { return ModInt(*this) -= that; }
	ModInt operator*(ModInt that) const { return ModInt(*this) *= that; }
};
typedef ModInt<1000000007> mint;

vector<vi> g;
 
vector<mint> dfs(int i, int j, bool first) {
	if(g[i].size() == j) {
		vector<mint> res(1 + first);
		res[0] = 1;
		if(first) res[1] = 1;
		return res;
	}
	vector<mint> left = dfs(g[i][j], 0, true);
	vector<mint> right = dfs(i, j+1, false);
	int leftsize = left.size() - 1, rightsize = right.size() - 1;

	vector<mint> res(leftsize + rightsize + first + 1);
	rep(k, leftsize + rightsize + 1) {
		mint x;
		int maxl = min(k, leftsize), minl = max(0, k - rightsize);
		for(int l = minl; l <= maxl; l ++)
			x += left[l] * right[k - l];
		res[k] += x;
		if(first && k == leftsize + rightsize)
			res[k+1] += x;
	}
//	cerr << i << ", " << j << ": "; rep(k, res.size()) cerr << res[k].get() << ", "; cerr << endl;
	return res;
}
 
int main() {
	int N, K;
	scanf("%d%d", &N, &K);
	if(K<0||K>N)return 1;
 
	g.assign(N, vi());
	rep(i, N-1) {
		int a, b;
		scanf("%d%d", &a, &b);
		if(a<0||a>=N||b<0||b>=N)return 1;
//		a=i+1,b=rand()%(i+1);swap(a,b);
		g[a].push_back(b);
	}
	return 0;

	vector<mint> v = dfs(0, 0, true);
	mint ans = K > N ? 0 : v[K];

	printf("%d\n", ans.get());
	return 0;
}