#include<bits/stdc++.h>
#define int long long
#define eb emplace_back
#define mp make_pair
#define DEBUG
using namespace std;
using pii = pair<int, int>;
using piii = pair<int, pii>;
using piiii = pair<pii, pii>;
using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned int;
const int P = 998244353;const i64 inf = 0x3f3f3f3f3f3f3f3f;
namespace azus{
	int clear();
	int n;
	vector<int> edge[500005];
	int du[500005], f[500005];
	vector<pii> ans;
	int dfs(int u, int fa){
		f[u] = u;
		vector<int> c;
		for(int v : edge[u]){
			if(v == fa) continue;
			dfs(v, u);
			c.eb(f[v]);
		}
		int x = c.size();
		for(int i = 0; i < x - 1; i += 2){
			ans.eb(mp(c[i], c[i + 1]));
		}
		if(x & 1){
			f[u] = c.back();
		}
		return 0;
	}
	int main(){
		clear();
		cin >> n;
		for(int i = 1; i < n; i ++){
			int u, v; cin >> u >> v;
			edge[u].eb(v), edge[v].eb(u);
			du[u] ++, du[v] ++;
		}
		int rt = -1;
		for(int i = 1; i <= n; i ++){
			if(!(du[i] & 1)) {
				rt = i; break;
			}
		}
		if(rt == -1){
			return cout << "-1\n", 0;
		}
		dfs(rt, 0);
		cout << ans.size() << "\n";
		for(auto [u, v] : ans) cout << u << " " << v << "\n";
		return 0;
	}
	int clear(){
		for(int i = 1; i <= n; i ++)
			edge[i].clear(), du[i] = 0, f[i] = 0;
		ans.clear();
		return 0;
	}
}
signed main(){
#ifndef DEBUG
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
#endif
	int T = 1;
	cin >> T;
	while(T --)
		azus::main();
	return 0;
}