#include<bits/stdc++.h> using namespace std; #define X first #define Y second #define mp make_pair #define pb push_back #define rep(i,a,n) for(int i=(a);i<=(n);++i) #define dep(i,a,n) for(int i=(a);i>=(n);--i) #define eps 1e-8 #define pi 3.1415926535897 #define sqr(x) ((x)*(x)) #define MAX(a,b) a=max(a,b) #define MIN(a,b) a=min(a,b) #define SZ(x) ((int)(x).size()) #define CPY(a,b) memcpy(a,b,sizeof(a)) #define CLR(a) memset(a,0,sizeof(a)) #define POSIN(x,y) (1<=(x)&&(x)<=n&&1<=(y)&&(y)<=m) #define all(x) (x).begin(),(x).end() #define COUT(S,x) cout<<fixed<<setprecision(x)<<S<<endl #define buli(x) (__builtin_popcountll(x)) #define bur0(x) (__builtin_ctzll(x)) #define bul2(x) (63-__builtin_clzll(x)) #define pw(x) ((ll(1))<<(x)) #define upmo(a,b) (((a)=((a)+(b))%mo)<0?(a)+=mo:(a)) #define mmo(a,b) (((a)=1ll*(a)*(b)%mo)<0?(a)+=mo:(a)) #define y0 y0z #define y1 y1z #define yn ynz #define j0 j0z #define j1 j1z #define jn jnz #define tm tmz #ifdef LOCAL #define debug(...) fprintf(stderr, __VA_ARGS__) #else #define debug(...) #endif typedef long long ll; typedef double lf; typedef pair<int,int> pii; typedef pair<ll,ll> pll; typedef pair<lf,lf> pff; typedef complex<double> CD; const int inf=0x3f3f3f3f; const int mo=1000000007; inline void gn(long long&x){ int sg=1;char c;while(((c=getchar())<'0'||c>'9')&&c!='-');c=='-'?(sg=-1,x=0):(x=c-'0'); while((c=getchar())>='0'&&c<='9')x=x*10+c-'0';x*=sg; } inline void gn(int&x){long long t;gn(t);x=t;} inline void gn(unsigned long long&x){long long t;gn(t);x=t;} inline void gn(double&x){double t;scanf("%lf",&t);x=t;} inline void gn(long double&x){double t;scanf("%lf",&t);x=t;} template<class T1,class T2>inline void gn(T1&r,T2&s){gn(r),gn(s);} template<class T1,class T2,class T3>inline void gn(T1&r,T2&s,T3&t){gn(r),gn(s),gn(t);} template<class T1,class T2,class T3,class T4>inline void gn(T1&r,T2&s,T3&t,T4&u){gn(r),gn(s),gn(t),gn(u);} inline void gs(char *s){scanf("%s",s);} inline void gc(char &c){while((c=getchar())>126 || c<33);} inline void pc(char c){putchar(c);} const int DX[]={1,0,-1,0},DY[]={0,1,0,-1}; ll powmod(ll a,ll b) {ll res=1;a%=mo;for(;b;b>>=1){if(b&1)res=res*a%mo;a=a*a%mo;}return res;} ll powmod(ll a,ll b,ll mo) {ll res=1;a%=mo;for(;b;b>>=1){if(b&1)res=res*a%mo;a=a*a%mo;}return res;} ll gcd(ll a,ll b) { return b?gcd(b,a%b):a;} //******************************************* const int N=111111,M=111111; int l,m,n,t,C,x,y; vector<int>a[N]; int fa[N]; vector<ll>MA[1011][1011][2]; void dfs(int x,int f){ for(auto i:a[x])if(i!=f)dfs(i,x); fa[x]=f; } void cal(int x,int y,int z){ if(SZ(MA[x][y][z]))return; vector<ll>V(m+1); if(y==0){ rep(i,0,m)V[i]=1; }else{ for(auto i:a[y])if(i!=x)cal(y,i,z); rep(i,1,m)V[i]=1; for(auto i:a[y])if(i!=x){ rep(j,1,m)V[j]=1ll*V[j]*MA[y][i][z][j]%mo; } rep(i,1,m)V[i]=(V[i]+V[i-1])%mo; } MA[x][y][z]=V; } ll calc(int x){ cal(x,fa[x],0); cal(fa[x],x,1); ll ans=0; rep(i,1,m)ans=(ans+1ll*MA[x][fa[x]][0][i-1]*(MA[fa[x]][x][1][i]-MA[fa[x]][x][1][i-1]+mo))%mo; // printf("%d %lld\n",x,ans); return ans; } int main(){ #ifdef LOCAL freopen("F.in","r",stdin);//freopen("F.out","w",stdout); #endif scanf("%d%d",&n,&m); rep(i,2,n)scanf("%d%d",&x,&y),a[x].pb(y),a[y].pb(x); dfs(1,0); ll ans=0; rep(i,1,n)ans=(ans+calc(i))%mo; ans=(ans+mo)%mo; cout<<ans<<endl; // for(auto i:MA){ // printf("%d %d %d: ",i.X.X.X,i.X.X.Y,i.X.Y); // rep(j,0,m)printf("%lld ",i.Y[j]);puts(""); // } return 0; }