#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
using namespace __gnu_pbds;
typedef long long int lld;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define trav(a,v) for(auto a:v)
vector<pair<int,lld> > nei[1000000];
int sz[1000000];
bool visited[1000000];
vector<pair<lld,lld> >V;
lld tot[1000000];

const lld INF=1e18;
const lld MOD=1e9+7;
const int MAX=3'000'000;
lld fact[MAX];
lld inv[MAX];
lld ModPow(lld base, lld exp){
	if(exp==0)return 1;
	if(exp%2==1)return (base*ModPow(base,exp-1))%MOD;
	lld a=ModPow(base,exp/2);
	return (a*a)%MOD;
}
lld comb(int a, int b){
	if(b<0 || b>a)return 0;
	lld ans=fact[a];
	ans*=inv[b];
	ans%=MOD;
	ans*=inv[a-b];
	ans%=MOD;
	return ans;
}
lld GCD(lld a, lld b){
	if(b==0)return a;
	return GCD(b,a%b);
}
const int Mx2=6000;
lld prd[Mx2];
int n;
void DFS(int node){
	visited[node]=true;
	sz[node]=1;
	trav(a,nei[node]){
		if(!visited[a.first]){
			DFS(a.first);
			tot[min(sz[a.first],n-sz[a.first])]+=a.second;
			sz[node]+=sz[a.first];
		}
	}
}
void solve(){
	int m;
	cin>>n>>m;
	
	rep(i,0,n-1){
		int x,y;
		lld l;
		cin>>x>>y>>l;
		x--;y--;
		nei[x].push_back({y,l});
		nei[y].push_back({x,l});
	}
	rep(i,0,n+1)tot[i]=0;
	DFS(0);
	lld ans=0;
	rep(i,1,n){
		lld conj=n-i;
		lld can=1;
		lld tot2=0;
		lld S=i*ModPow(conj,MOD-2);
		S%=MOD;
		lld CurPow=ModPow(conj,2*m);
		rep(c,0,2*m+1){
			lld par=min(c,2*m-c);
			lld tot3=CurPow;
			tot3%=MOD;
			tot3*=comb(2*m,c);
			tot3%=MOD;
			CurPow*=S;
			CurPow%=MOD;
			//~ rep(a,0,c+1){
				//~ lld b=c-a;
				//~ if(0<=a && a<=m && 0<=b && b<=m){
					
				//~ }else continue;
				//~ lld par2=ModPow(i,a)*ModPow(i,b);
				//~ par2%=MOD;
				//~ par2*=ModPow(conj,m-a);
				//~ par2%=MOD;
				//~ par2*=comb(m,a);
				//~ par2%=MOD;
				//~ par2*=ModPow(conj,m-b);
				//~ par2%=MOD;
				//~ par2*=comb(m,b);
				//~ par2%=MOD;
				//~ tot3+=par2;
				//~ tot3%=MOD;
			//~ }
			//cout<<tot3<<" A "<<c<<" "<<i<<endl;
			tot2+=tot3*par;
			tot2%=MOD;
		}
		//cout<<i<<" "<<tot2<<"\n";
		can*=tot2;
		can%=MOD;
		ans+=can*tot[i];
		ans%=MOD;
	}
	cout<<ans<<"\n";
}

int main(){
	fact[0]=1;
	rep(i,1,MAX)fact[i]=(i*fact[i-1])%MOD;
	inv[MAX-1]=ModPow(fact[MAX-1],MOD-2);
	for(int i=MAX-2;i>-1;i--)inv[i]=((i+1)*inv[i+1])%MOD;
	//~ rep(i,0,Mx2){
		//~ rep(j,0,Mx2){
			//~ if(j==0)Q[i][j]=1;
			//~ else{
				//~ if(i==0)Q[i][j]=0;
				//~ else{
					//~ Q[i][j]=(Q[i-1][j]+j*Q[i][j-1]);
					//~ Q[i][j]%=MOD;
				//~ }
			//~ }
			//~ Q[i][j]=ModPow(i,j)*(j+1);
			//~ Q[i][j]%=MOD;
		//~ }
	//~ }
	ios::sync_with_stdio(0);
	cin.tie(0);
	int tt=1;
	//cin>>tt;
	while(tt--){
		solve();
	}
}