#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <map>
#include <set>
#include <cmath>
#include <bitset>
#include <cassert>
#include <numeric>

using namespace std;
typedef long long ll;

const int N = 300010;

int n;
vector<int> edge[N];
bool f[N][2];
int g[N];
vector<pair<int, int>> e;

void dfs(int u, int father)
{
	int cnt_son = 0;
	for (int v : edge[u])
	{
		if (v == father) continue;
		cnt_son ++;
	}

	if (cnt_son & 1) f[u][1] = true;
	else f[u][0] = true;

	for (int v : edge[u])
	{
		if (v == father) continue;
		dfs(v, u);
		if (cnt_son & 1)
		{
			if (f[v][1]) f[u][0] = true, g[u] = v;
		}
		else 
		{
			if (f[v][1]) f[u][1] = true, g[u] = v;
		}
	}
}

int dfs2(int u, int st, int father)
{
	int cnt_son = 0;
	for (int v : edge[u])
	{
		if (v == father) continue;
		cnt_son ++;
	}

	if ((cnt_son & 1) && st)
	{
		vector<int> son;
		for (int v : edge[u])
		{
			if (v == father) continue;
			son.push_back(v);
		}

		for (int i = 1; i < son.size(); i += 2)
		{
			int v1 = son[i], v2 = son[i + 1];
			int s1, s2;
			if (f[v1][0]) s1 = dfs2(v1, 0, u);
			else s1 = dfs2(v1, 1, u);
			if (f[v2][0]) s2 = dfs2(v2, 0, u);
			else s2 = dfs2(v2, 1, u);
			e.push_back({s1, s2});
		}

		int v = son[0];
		if (f[v][0]) return dfs2(v, 0, u);
		else return dfs2(v, 1, u);
	}
	else if ((cnt_son & 1) && !st)
	{
		vector<int> son;
		for (int v : edge[u])
		{
			if (v == father) continue;
			if (v != g[u]) son.push_back(v);
		}

		for (int i = 0; i < son.size(); i += 2)
		{
			int v1 = son[i], v2 = son[i + 1];
			int s1, s2;
			if (f[v1][0]) s1 = dfs2(v1, 0, u);
			else s1 = dfs2(v1, 1, u);
			if (f[v2][0]) s2 = dfs2(v2, 0, u);
			else s2 = dfs2(v2, 1, u);
			e.push_back({s1, s2});
		}

		int s = dfs2(g[u], 1, u);
		e.push_back({u, s});
		return u;
	}
	else if (!(cnt_son & 1) && !st)
	{
		vector<int> son;
		for (int v : edge[u])
		{
			if (v == father) continue;
			son.push_back(v);
		}

		for (int i = 0; i < son.size(); i += 2)
		{
			int v1 = son[i], v2 = son[i + 1];
			int s1, s2;
			if (f[v1][0]) s1 = dfs2(v1, 0, u);
			else s1 = dfs2(v1, 1, u);
			if (f[v2][0]) s2 = dfs2(v2, 0, u);
			else s2 = dfs2(v2, 1, u);
			e.push_back({s1, s2});
		}

		return u;
	}
	else 
	{
		vector<int> son;
		for (int v : edge[u])
		{
			if (v == father) continue;
			if (v != g[u]) son.push_back(v);
		}

		for (int i = 1; i < son.size(); i += 2)
		{
			int v1 = son[i], v2 = son[i + 1];
			int s1, s2;
			if (f[v1][0]) s1 = dfs2(v1, 0, u);
			else s1 = dfs2(v1, 1, u);
			if (f[v2][0]) s2 = dfs2(v2, 0, u);
			else s2 = dfs2(v2, 1, u);
			e.push_back({s1, s2});
		}

		int s = dfs2(g[u], 1, u);
		e.push_back({u, s});
		
		int v = son[0];
		if (f[v][0]) return dfs2(v, 0, u);
		else return dfs2(v, 1, u);
	}
}

void solve()
{
	cin >> n;
	for (int i = 1; i <= n; i ++)
		edge[i].clear(), f[i][0] = f[i][1] = false;

	for (int i = 0; i < n - 1; i ++)
	{
		int u, v;
		cin >> u >> v;
		edge[u].push_back(v);
		edge[v].push_back(u);
	}	

	dfs(1, 0);
	if (!f[1][0])
	{
		cout << "-1\n";
		return;
	}

	e.clear();
	dfs2(1, 0, 0);
	cout << e.size() << '\n';
	for (auto [u, v] : e)
		cout << u << ' ' << v << '\n';
}

int main()
{
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);

	int tt = 1;
	cin >> tt;
	while (tt --)
	{
		solve();
	}
	return 0;
}