#include <set>
#include <map>
#include <cmath>
#include <queue>
#include <ctime>
#include <cstdio>
#include <random>
#include <vector>
#include <bitset>
#include <cassert>
#include <cstring>
#include <algorithm>
#define fi first
#define se second
#define MISAKA main
#define ll long long
#define eb emplace_back
#define pii pair<int,int>
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define _rep(i,a,b) for(int i=(a);i>=(b);--i)
#define debug(...) fprintf(stderr,__VA_ARGS__)
#define FIO(FILE) freopen(FILE".in","r",stdin),freopen(FILE".out","w",stdout)
using namespace std;
inline int read(){
    char ch=getchar();int f=1,x=0;
    while(ch<'0'||ch>'9'){if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+(ch^48);ch=getchar();}
    return x*f;
}
const int N=5e5+10,mod=998244353;
int n,m,dfn[N],id[N],d[N],dep[N],top[N],fa[N],son[N],now[N],siz[N],cl[N],tim;
vector<int> g[N];
struct node{int x,y,id;
    node(int a=0,int b=0,int c=0){x=a,y=b,id=c;}
};vector<node> vt[N];
void dfs1(int u,int f){
    fa[u]=f,dep[u]=dep[f]+1,siz[u]=1;
    for(int v:g[u])if(v!=f){
        dfs1(v,u),siz[u]+=siz[v];
        if(siz[v]>siz[son[u]]) son[u]=v;
    }
}
void dfs2(int u,int tp){
    top[u]=tp,id[dfn[u]=++tim]=u;
    if(son[u]) dfs2(son[u],tp);
    for(int v:g[u])if(v!=son[u]&&v!=fa[u]) dfs2(v,v);
}
int lca(int x,int y){
    for(;top[x]^top[y];x=fa[top[x]])
        if(dep[top[x]]<dep[top[y]]) swap(x,y);
    return dep[x]<dep[y]?x:y;
}
void dfs3(int u){for(int v:g[u])if(v!=fa[u]) dfs3(v),d[u]+=d[v];}
struct segtree{int l,r,t;pii v;}t[N<<2];
void pu(int x){t[x].v=max(t[2*x].v,t[2*x+1].v);}
void bd(int x,int l,int r){
    t[x].l=l,t[x].r=r,t[x].t=0;int mid=l+r>>1;
    if(l==r){t[x].v={d[id[l]],-l};return;}
    bd(2*x,l,mid);bd(2*x+1,mid+1,r);pu(x);
}
void cal(int x,int k){t[x].v.fi+=k,t[x].t+=k;}
void pd(int x){if(t[x].t)cal(2*x,t[x].t),cal(2*x+1,t[x].t),t[x].t=0;}
void upd(int x,int l,int r,int k){
    if(t[x].r<l||t[x].l>r) return;
    if(l<=t[x].l&&t[x].r<=r) return cal(x,k);
    pd(x);upd(2*x,l,r,k);upd(2*x+1,l,r,k);pu(x);
}
void upd(int x,int y,int k){
    for(;top[x]^top[y];x=fa[top[x]]){
        if(dep[top[x]]<dep[top[y]]) swap(x,y);
        upd(1,dfn[top[x]],dfn[x],k);
    }
    if(dfn[x]>dfn[y]) swap(x,y);
    upd(1,dfn[x],dfn[y],k);
}
void misaka(){
    rep(i,1,n) g[i].clear(),vt[i].clear(),now[i]=d[i]=dfn[i]=id[i]=siz[i]=son[i]=fa[i]=dep[i]=top[i]=cl[i]=0;tim=0;
    n=read(),m=read();
    rep(i,2,n){
        int u=read(),v=read();
        g[u].eb(v);g[v].eb(u);
    }   
    dfs1(1,0);dfs2(1,1);
    rep(i,1,m){
        int u=read(),v=read(),l=lca(u,v);
        vt[l].eb(u,v,i);
        d[u]++,d[v]++,d[l]--,d[fa[l]]--;
    }
    dfs3(1);bd(1,1,n);
    printf("%d\n",t[1].v.fi);
    while(t[1].v.fi){
        int x=id[-t[1].v.se];
        node k=vt[x][now[x]++];
        cl[k.id]=t[1].v.fi;
        upd(k.x,k.y,-1);
    }
    rep(i,1,m) printf("%d ",cl[i]);puts("");
}
signed MISAKA(){
    read();int T=read();
    while(T--) misaka();
    return 0;
}