#include<bits/stdc++.h>
using namespace std;
#define pb emplace_back
using ll=long long;
using pii=pair<int,int>;
const ll mod=1e9+7;
ll ksm(ll a,ll b)
{
	ll ans=1;
	while(b)
	{
		if(b&1) ans=ans*a%mod;
		b>>=1;
		a=a*a%mod;
	}
	return ans;
}
ll C[3003][3003];
vector<pii> G[3003];
int siz[3003];
int n,m;
ll calc(int s)
{
	ll p=s*ksm(n-s,mod-2);
	ll q=ksm(p,mod-2);
	ll ret=ksm(s*(n-s),m);
	ll tot1=0,tot2=0;
	ll tmp1=1,tmp2=1;
	vector<ll> val1(m+1),val2(m+1);
	for(int i=0;i<=m;i++)
	{
		tot1=(tot1+(val1[i]=C[m][i]*tmp1%mod))%mod;
		tot2=(tot2+(val2[i]=C[m][i]*tmp2%mod))%mod;
		tmp1=tmp1*p%mod;
		tmp2=tmp2*q%mod;
	}
	ll ans=tot1*tot2%mod*m%mod;
	vector<ll> val3=val1,val4=val2;
	for(int i=1;i<=m;i++)
		val1[i]=(val1[i]+val1[i-1])%mod;
	for(int i=1;i<=m;i++)
		val2[i]=(val2[i]+val2[i-1])%mod;
	for(int i=m;i;i--)
		val3[i-1]=(val3[i-1]+val3[i])%mod;
	for(int i=m;i;i--)
		val4[i-1]=(val4[i-1]+val4[i])%mod;
	for(int i=1;i<=m;i++)
		ans=(ans-val1[i-1]*val4[i]%mod+mod)%mod;
	for(int i=1;i<=m;i++)
		ans=(ans-val2[i-1]*val3[i]%mod+mod)%mod;
	return ans*ret%mod;
}
ll ans;
void dfs(int u,int fa)
{
	siz[u]=1;
	for(auto [v,w]:G[u])
		if(v!=fa)
		{
			dfs(v,u);
			ans=(ans+w*calc(siz[v]))%mod;
			siz[u]+=siz[v];
		}
}
int main()
{
	for(int i=0;i<3003;i++)
		C[i][i]=C[i][0]=1;
	for(int i=2;i<3003;i++)
		for(int j=1;j<i;j++)
			C[i][j]=(C[i-1][j]+C[i-1][j-1])%mod;
	cin>>n>>m;
	for(int i=1;i<n;i++)
	{
		int u,v,l;
		cin>>u>>v>>l;
		G[u].pb(v,l);
		G[v].pb(u,l);
	}
	dfs(1,0);
	cout<<ans<<'\n';
	return 0;
}