#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 1e5 + 10;
const int MOD = 998244353;
const int inf = 1e9 + 7;
#define PII pair<int,int>
#define endl "\n"


void solve(){
	int n;
	cin >> n;
	vector<vector<int>> g(n+10);
	for( int i = 1 ; i < n ; i++ ){
		int u , v;
		cin >> u >> v;
		g[u].push_back(v);
		g[v].push_back(u);
	}
	vector<vector<PII>> dp(n+10,vector<PII>(2,{0,0}));
	auto debug = [&](int u){
		cout << dp[u][0].first << " " << dp[u][0].second << endl;
		cout << dp[u][1].first << " " << dp[u][1].second << endl;
	};
	vector<vector<map<PII,PII>>> tp(n+10,vector<map<PII,PII>>(2));
	vector<vector<int>> e(n+10,vector<int>(2,-1));
	function<void(int,int)> dfs = [&](int u,int p){
		vector<PII> t;
		int cnt0 = 0 , cnt1 = 0;
		for( auto v : g[u] ){
			if( v == p ) continue;
			dfs(v,u);
			if( dp[v][1] != make_pair(0,0) ) t.push_back({v,1}) , cnt1++; 
			else t.push_back({v,0}) , cnt0++;
		}	
		sort(t.begin(),t.end(),[&](auto a,auto b){
			return a.second > b.second;	
		});
		int sum = cnt0 + cnt1;
//		cout << u << " " << sum << endl;
		if( sum == 0 ){
			dp[u][0] = {u,0};
			dp[u][1] = {0,0};
			
		}
		else {
			if( sum & 1 ){ // 奇数个点
				dp[u][1] = dp[t[0].first][t[0].second]; // 更新不自洽点，dp记录哪一个点
				tp[u][1][t[0]] = {0,0};
				for( int i = 1 ; i < t.size() ; i += 2 ) tp[u][1][t[i]] = t[i+1];
				if( cnt1 ){ // 更新自洽，一定是u连接儿子的不自洽点
					dp[u][0] = {u,0};
					e[u][0] = dp[t[0].first][1].first;
					tp[u][0][t[0]] = {0,0};
					for( int i = 1 ; i < t.size() ; i += 2 ) tp[u][0][t[i]] = t[i+1];
				}
			}
			else { // 偶数
				dp[u][0] = {u,0}; // 自洽，直接儿子两两相连
				for( int i = 0 ; i < t.size() ; i += 2 ) tp[u][0][t[i]] = t[i+1];
				if( cnt1 ){ // 不自洽，一定是儿子中的不自洽点连到u，其他两两相连，剩下一个作为不自洽
					e[u][1] = dp[t[0].first][t[0].second].first; // 我连了谁
					dp[u][1] = dp[t[1].first][t[1].second]; // 我代表谁
					tp[u][1][t[0]] = {0,0};
					tp[u][1][t[1]] = {0,0};
					for( int i = 2 ; i < t.size() ; i += 2 ) tp[u][1][t[i]] = t[i+1];
				}
			}
		}
	};
	dfs(1,0);
	if( dp[1][0] == make_pair(0,0) ){
		cout << -1 << endl;	
	}
	else {
		queue<PII> q;
		q.push({1,0});
		vector<pair<int,int>> op;
		while( q.size() ){
			auto [u,id] = q.front(); q.pop();
			if( e[u][id] != -1 ) {
				op.push_back({u,e[u][id]});
			}
			for( auto [key,val] : tp[u][id] ){
				q.push(key);
				if( val != make_pair(0,0) ){
					q.push(val);
					op.push_back({dp[key.first][key.second].first,dp[val.first][val.second].first});
				} 
			}
		}
		cout << op.size() << endl;
		for( auto [u,v] : op ){
			cout << u << " " << v << endl;
		}
	}
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int t;
	cin >> t;
	while(t--) solve();
	return 0;
}