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

#define int long long

#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,a,b) for(int i=(a);i<(b);i++)
#define pb push_back
#define eb emplace_back
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second

using vint=vector<int>;
using pint=pair<int,int>;
using vpint=vector<pint>;

template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

template<class A,class B>
ostream& operator<<(ostream& ost,const pair<A,B>&p){
    ost<<"{"<<p.first<<","<<p.second<<"}";
    return ost;
}

template<class T>
ostream& operator<<(ostream& ost,const vector<T>&v){
    ost<<"{";
    for(int i=0;i<v.size();i++){
        if(i)ost<<",";
        ost<<v[i];
    }
    ost<<"}";
    return ost;
}

template<uint32_t mod>
struct ModInt{
    uint32_t a;
    ModInt& s(uint32_t vv){
        a=vv<mod?vv:vv-mod;
        return *this;
    }

    ModInt(int64_t x=0){s(x%mod+mod);}

    ModInt& operator+=(const ModInt &x){return s(a+x.a);}
    ModInt& operator-=(const ModInt &x){return s(a+mod-x.a);}
    ModInt& operator*=(const ModInt &x){
        a=uint64_t(a)*x.a%mod;
        return *this;
    }
    ModInt& operator/=(const ModInt &x){
        *this*=x.inv();
        return *this;
    }

    ModInt operator+(const ModInt &x)const{return ModInt(*this)+=x;}
    ModInt operator-(const ModInt &x)const{return ModInt(*this)-=x;}
    ModInt operator*(const ModInt &x)const{return ModInt(*this)*=x;}
    ModInt operator/(const ModInt &x)const{return ModInt(*this)/=x;}
    bool operator==(const ModInt &x)const{return a==x.a;}
    bool operator!=(const ModInt &x)const{return a!=x.a;}
    bool operator<(const ModInt &x)const{return a<x.a;}

    ModInt operator-()const{return ModInt()-*this;}
    ModInt pow(int64_t n)const{
        ModInt res(1),x(*this);
        while(n){
            if(n&1)res*=x;
            x*=x;
            n>>=1;
        }
        return res;
    }

    ModInt inv()const{return pow(mod-2);}
};

template<uint32_t mod>
istream& operator>>(istream& in,const ModInt<mod>& a){
    return (in>>a.a);
}
template<uint32_t mod>
ostream& operator<<(ostream& out,const ModInt<mod>& a){
    return (out<<a.a);
}
using mint=ModInt<1000000007>;

template<class Mint,int32_t lg>
struct ModIntTable{
	int N;
	vector<Mint>facts,finvs,invs;
	ModIntTable():N(1<<lg),facts(N),finvs(N),invs(N){
		const uint32_t mod=Mint(-1).a+1;
		invs[1]=1;
		for(int i=2;i<N;i++)invs[i]=invs[mod%i]*(mod-mod/i);

		facts[0]=1;
		finvs[0]=1;
		for(int i=1;i<N;i++){
			facts[i]=facts[i-1]*i;
			finvs[i]=finvs[i-1]*invs[i];
		}
	}
	inline Mint fact(int n)const{return facts[n];}
	inline Mint finv(int n)const{return finvs[n];}
	inline Mint inv(int n)const{return invs[n];}
	inline Mint binom(int n,int k)const{return facts[n]*finvs[k]*finvs[n-k];}
};
ModIntTable<mint,19>mtable;

int N,K;
vint G[111111];

mint dfs(int v,int p){
    int c=G[v].size()-1;
    if(c+2>K)return 0;
    mint ret=mtable.fact(K-2)*mtable.finv(K-2-c);
    for(auto &u:G[v]){
        if(u==p)continue;
        ret*=dfs(u,v);
    }
    return ret;
}
signed main(){
    scanf("%lld%lld",&N,&K);
    rep(i,N-1){
        int a,b;
        scanf("%lld%lld",&a,&b);
        a--;b--;
        G[a].pb(b);
        G[b].pb(a);
    }

    if(G[0].size()+1>K){
        cout<<0<<endl;
        return 0;
    }

    mint ans=mtable.fact(K)*mtable.finv(K-G[0].size()-1);
    for(auto &u:G[0]){
        ans*=dfs(u,0);
    }
    cout<<ans<<endl;
    return 0;
}

Measured memory_bytes: 16768