#include<bits/stdc++.h>
using namespace std;
using ll = long long;

vector<pair<int,int>> ans;
vector<int> G[300300];
const int INF = 1<<30;

int dfs(int v, int p=-1){
	bool done = 1;
	if((int)G[v].size() % 2 == 1){
		done = 0;
	}
	int memo = -1;
	for(auto c:G[v]){
		if(c == p)continue;
		int tmp = dfs(c, v);
		if(tmp == -1)continue;
		if(!done && tmp != c){
			ans.push_back(make_pair(v, tmp));
			done = 1;
			continue;
		}
		if(memo != -1){
			ans.push_back(make_pair(memo, tmp));
			memo = -1;
		}
		else{
			memo = tmp;
		}
	}
	if(!done && v == 0){
		ans.push_back(make_pair(INF, INF));
	}
	if(!done)memo = v;
	return memo;
}



void solve(){
	int N; cin >> N;
	for(int i = 0; i < N; i++)G[i].clear();
	ans.clear();
	for(int i = 0; i < N-1; i++){
		int a,b; cin >> a >> b;
		--a; --b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	dfs(0);
	if(ans.back().first == INF)cout << -1 << endl;
	else{
		cout << (int)ans.size() << endl;
		for(auto p:ans){
			cout << p.first+1 << ' ' << p.second+1 << endl;
		}
	}
}

int main(){
	int T; cin >> T;
	while(T--){
		solve();
	}
}