#include<bits/stdc++.h>
using namespace std;using ld=long double;using ll=long long;
using pll=pair<ll,ll>;
const int M=1e9+7,N=5e3+10,inv2=(M+1)/2,P=20;const ld eps=1e-8,pi=acos(-1);
ll poww(ll bs,ll x){ll res=1;for(;x;x>>=1,(bs*=bs)%=M)if(x&1)(res*=bs)%=M;return res;}
ll invv(ll bs){return poww(bs,M-2);}
ll C[N+1][N+1];
struct S
{
    int n,m;ll res=0;
    struct edg{int u,v,w;};
    vector<vector<int>>es;vector<edg>E;
    int spr(int x,int le)
    {
        int sz=1;for(auto&k:es[x])if(k^le)
        {
            int des=E[k].u^E[k].v^x;sz+=spr(des,k);
        }
        if(!le)return sz;
        int sA=sz,sB=n-sz;
        //cout<<le<<":"<<sA<<'/'<<sB<<":"<<E[le].w<<'\n';
        for(int lc=0,rc;lc<=m*2;lc++)
        {
            rc=m*2-lc;
            ll A=poww(sA,lc),B=poww(sB,rc);
            (res+=A*B%M*C[m*2][lc]*min(lc,rc)%M*E[le].w%M)%=M;
        }
        return sz;
    }
    void ini()
    {
         cin>>n>>m;es.resize(n+1);E.resize(n);
         for(int i=1;i<n;i++)
         {
             auto&[u,v,w]=E[i];cin>>u>>v>>w;
             es[u].push_back(i);es[v].push_back(i);
         }
         spr(1,0);cout<<res<<'\n';
    }
    void solve()
    {

    }
};
void precal()
{
    for(int i=0;i<=N;i++)for(int j=0;j<=i;j++)
        C[i][j]=j?(C[i-1][j]+C[i-1][j-1])%M:1;
}
signed main()
{
    cout<<fixed<<setprecision(12);
    ios::sync_with_stdio(0);
    cin.tie(0);precal();
    int t=1;//cin>>t;
    while(t--){S SS;SS.ini();SS.solve();}
}
/*
5 2
4 5 199
3 4 20
2 3 0
1 3 0
 */