#line 1 "a.cpp"
#include<iostream>
#include<vector>
using namespace std;
#line 3 "/home/kotatsugame/library/math/modint.cpp"
#include<utility>
template<int m>
struct modint{
	unsigned int x;
	constexpr modint()noexcept:x(){}
	constexpr modint(long long _x)noexcept:x((_x%=m)<0?_x+m:_x){}
	constexpr unsigned int val()const noexcept{return x;}
	constexpr modint&operator++()noexcept{if(++x==m)x=0;return*this;}
	constexpr modint&operator--()noexcept{if(x==0)x=m;--x;return*this;}
	constexpr modint operator++(int)noexcept{modint res=*this;++*this;return res;}
	constexpr modint operator--(int)noexcept{modint res=*this;--*this;return res;}
	constexpr modint&operator+=(const modint&a)noexcept{x+=a.x;if(x>=m)x-=m;return*this;}
	constexpr modint&operator-=(const modint&a)noexcept{if(x<a.x)x+=m;x-=a.x;return*this;}
	constexpr modint&operator*=(const modint&a)noexcept{x=(unsigned long long)x*a.x%m;return*this;}
	constexpr modint&operator/=(const modint&a)noexcept{return*this*=a.inv();}
	constexpr modint operator+()const noexcept{return*this;}
	constexpr modint operator-()const noexcept{return modint()-*this;}
	constexpr modint pow(long long n)const noexcept
	{
		if(n<0)return pow(-n).inv();
		modint x=*this,r=1;
		for(;n;x*=x,n>>=1)if(n&1)r*=x;
		return r;
	}
	constexpr modint inv()const noexcept
	{
		int s=x,t=m,x=1,u=0;
		while(t)
		{
			int k=s/t;
			s-=k*t;
			swap(s,t);
			x-=k*u;
			swap(x,u);
		}
		return modint(x);
	}
	friend constexpr modint operator+(const modint&a,const modint&b){return modint(a)+=b;}
	friend constexpr modint operator-(const modint&a,const modint&b){return modint(a)-=b;}
	friend constexpr modint operator*(const modint&a,const modint&b){return modint(a)*=b;}
	friend constexpr modint operator/(const modint&a,const modint&b){return modint(a)/=b;}
	friend constexpr modint operator==(const modint&a,const modint&b){return a.x==b.x;}
	friend constexpr modint operator!=(const modint&a,const modint&b){return a.x!=b.x;}
	friend ostream&operator<<(ostream&os,const modint&a){return os<<a.x;}
	friend istream&operator>>(istream&is,modint&a){long long v;is>>v;a=modint(v);return is;}
};
#line 5 "a.cpp"
using mint=modint<(int)1e9+7>;
int N,K;
vector<int>G[2000];
mint dp[2000][2001];
int dfs(int u,int p)
{
	int ch=0;
	dp[u][0]=1;
	for(int v:G[u])if(v!=p)
	{
		int x=dfs(v,u);
		for(int i=ch;i>=0;i--)
		{
			mint now=dp[u][i];
			dp[u][i]=0;
			for(int j=0;j<=x;j++)dp[u][i+j]+=now*dp[v][j];
		}
		ch+=x;
	}
	dp[u][++ch]=1;
	return ch;
}
main()
{
	cin>>N>>K;
	for(int i=1;i<N;i++)
	{
		int a,b;cin>>a>>b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	dfs(0,-1);
	cout<<dp[0][K]<<endl;
}