//code by Emissary
#include<bits/stdc++.h>

#define fi first
#define se second
#define vc vector
#define db double
#define ll long long
#define mk make_pair
#define pb push_back
#define PI pair<int,int>
#define ull unsigned long long
#define err cerr << "   -_-   " << endl
#define debug cerr << " ------------------- " << endl

#define input(x) freopen(#x".in","r",stdin)
#define output(x) freopen(#x".out","w",stdout)

#define NO puts("No")
#define YES puts("Yes")

//#define int long long

using namespace std;

namespace IO{
	inline int read(){
		int X=0, W=0; char ch=getchar();
		while(!isdigit(ch)) W|=ch=='-', ch=getchar();
		while(isdigit(ch)) X=(X<<1)+(X<<3)+(ch^48), ch=getchar();
		return W?-X:X;
	}
	inline void write(ll x){
		if(x<0) x=-x, putchar('-');
		if(x>9) write(x/10);
		putchar(x%10+'0');
	}
	inline void sprint(ll x){write(x), putchar(32);}
	inline void eprint(ll x){write(x), putchar(10);}
}using namespace IO;

const int MAXN = 3e5+5;

int n, m, sum[MAXN], type[MAXN];
int ta[MAXN], tb[MAXN], siz[MAXN], tp[MAXN];
int head[MAXN], ne[MAXN<<1], to[MAXN<<1], de[MAXN], cnt;

set<PI> num[MAXN];

ll minans;

vc<int> ans;

inline void add(int x, int y){++cnt;to[cnt]=y;ne[cnt]=head[x];head[x]=cnt;}

inline void dfs(int x, int f){
	siz[x]=(ta[x]?1:0)-(tb[x]?1:0); sum[x]=(ta[x]?1:0)+(tb[x]?1:0); de[x]=de[f]+1;
	for(int i=head[x];i;i=ne[i]){
		if(to[i]==f) continue;
		dfs(to[i],x); siz[x]+=siz[to[i]]; sum[x]+=sum[to[i]];
		if(!sum[to[i]]) continue;
		minans+=max(2,abs(siz[to[i]])*2);
	}
	return ;
}

inline void construct(int x, int f){
	type[x]=1;
	for(int i=head[x];i;i=ne[i]){
		if(to[i]==f) continue;
		if(siz[to[i]]<0) continue;
		construct(to[i],x);
		if(type[to[i]]!=type[x]){
			if(num[x].size()>num[to[i]].size()) swap(num[x],num[to[i]]), swap(type[x],type[to[i]]);
			while(num[x].size()){
				if(type[x]==1) ans.pb((*num[x].rbegin()).se), ans.pb((*num[to[i]].rbegin()).se);
				else ans.pb((*num[to[i]].rbegin()).se), ans.pb((*num[x].rbegin()).se);
				num[x].erase(*num[x].rbegin()); num[to[i]].erase(*num[to[i]].rbegin());
			}
			swap(num[x],num[to[i]]); type[x]=type[to[i]];
		}
		else{
			if(num[x].size()<num[to[i]].size()) swap(num[x],num[to[i]]);
			for(auto j:num[to[i]]) num[x].insert(j);
		}
	}
	for(int i=head[x];i;i=ne[i]){
		if(to[i]==f) continue;
		if(siz[to[i]]>=0) continue;
		construct(to[i],x);
		if(type[to[i]]!=type[x]){
			if(num[x].size()>num[to[i]].size()) swap(num[x],num[to[i]]), swap(type[x],type[to[i]]);
			while(num[x].size()){
				if(type[x]==1) ans.pb((*num[x].rbegin()).se), ans.pb((*num[to[i]].begin()).se);
				else ans.pb((*num[to[i]].begin()).se), ans.pb((*num[x].rbegin()).se);
				num[x].erase(*num[x].rbegin()); num[to[i]].erase(*num[to[i]].begin());
			}
			swap(num[x],num[to[i]]); type[x]=type[to[i]];
		}
		else{
			if(num[x].size()<num[to[i]].size()) swap(num[x],num[to[i]]);
			for(auto j:num[to[i]]) num[x].insert(j);
		}
	}
	if(ta[x]){
		if(num[x].size()==0) num[x].insert(mk(de[x],ta[x])), type[x]=1;
		else{
			if(type[x]==1) num[x].insert(mk(de[x],ta[x]));
			else{
				ans.pb(ta[x]); ans.pb((*num[x].rbegin()).se); num[x].erase(*num[x].rbegin());
			}
		}
	}
	if(tb[x]){
		if(num[x].size()==0) num[x].insert(mk(de[x],tb[x])), type[x]=2;
		else{
			if(type[x]==2) num[x].insert(mk(de[x],tb[x]));
			else{
				ans.pb((*num[x].rbegin()).se); ans.pb(tb[x]); num[x].erase(*num[x].rbegin());
			}
		}
	}
	tp[x]=type[x];
	return ;
}

signed main(){
	n=read(), m=read();
	for(int i=1;i<=m;++i) ta[read()]=i;
	for(int i=1;i<=m;++i) tb[read()]=i;
	for(int i=2;i<=n;++i){
		int x, y;
		x=read(), y=read();
		add(x,y), add(y,x);
	}
	dfs(1,0); construct(1,0);
	eprint(minans);
	for(auto i:ans) sprint(i);
	return 0;
}