// 長い夜の終わりを信じながら
// Think twice, code once.
#include <vector>
#include <cstdio>
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
#define eputchar(c) putc(c, stderr)
#define eprintf(...) fprintf(stderr, __VA_ARGS__)
#define eputs(str) fputs(str, stderr), putc('\n', stderr)
using namespace std;

int T, n, dp[300005][3];
struct graph {
	int tot, hd[300005];
	int nxt[600005], to[600005];

	void clear(int n) {tot = 0; memset(hd, 0, sizeof(int) * n); return;}
	void add(int u, int v) {
		nxt[++tot] = hd[u];
		hd[u] = tot;
		to[tot] = v;
		return;
	}
} g;
vector<pair<int, int>> ans;

void dfs(int now, int fa) {
	dp[now][0] = dp[now][1] = dp[now][2] = 0;
	int num0 = 0, num1 = 0;
	for (int i = g.hd[now]; i; i = g.nxt[i])
		if (g.to[i] != fa) {
			dfs(g.to[i], now);
			if (dp[g.to[i]][1] || dp[g.to[i]][2]) num1++;
			else num0++;
		}
	dp[now][0] = num0 % 2 == 0 || num1;
	for (int i = g.hd[now]; i; i = g.nxt[i])
		if (g.to[i] != fa) {
			int n0 = num0, n1 = num1;
			if (dp[g.to[i]][1] || dp[g.to[i]][2]) n1--;
			else n0--;
			if (dp[g.to[i]][0]) dp[now][1] |= n0 % 2 == 0 || n1;
			if (dp[g.to[i]][1]) dp[now][2] |= n0 % 2 == 0 || n1;
		}
	return;
}
void solve(int, const vector<int> &);
int getans(int now, int fa, int o) {
	int num0 = 0, num1 = 0;
	for (int i = g.hd[now]; i; i = g.nxt[i])
		if (g.to[i] != fa) {
			if (dp[g.to[i]][1] || dp[g.to[i]][2]) num1++;
			else num0++;
		}
	vector<int> sons;
	if (o == 0) {
		for (int i = g.hd[now]; i; i = g.nxt[i])
			if (g.to[i] != fa) sons.push_back(g.to[i]);
		solve(now, sons);
		return now;
	} else if (o == 1) {
		int son = -1;
		for (int i = g.hd[now]; i; i = g.nxt[i])
			if (g.to[i] != fa) {
				int n0 = num0, n1 = num1;
				if (dp[g.to[i]][1] || dp[g.to[i]][2]) n1--;
				else n0--;
				if (dp[g.to[i]][0] && (n0 % 2 == 0 || n1)) {son = g.to[i]; break;}
			}
		for (int i = g.hd[now]; i; i = g.nxt[i])
			if (g.to[i] != fa && g.to[i] != son) sons.push_back(g.to[i]);
		solve(now, sons);
		return getans(son, now, 0);
	} else {
		int son = -1;
		for (int i = g.hd[now]; i; i = g.nxt[i])
			if (g.to[i] != fa) {
				int n0 = num0, n1 = num1;
				if (dp[g.to[i]][1] || dp[g.to[i]][2]) n1--;
				else n0--;
				if (dp[g.to[i]][1] && (n0 % 2 == 0 || n1)) {son = g.to[i]; break;}
			}
		for (int i = g.hd[now]; i; i = g.nxt[i])
			if (g.to[i] != fa && g.to[i] != son) sons.push_back(g.to[i]);
		solve(now, sons);
		return getans(son, now, 1);
	}
}
void solve(int now, const vector<int> &sons) {
	int lst = -1;
	vector<int> vec;
	for (int i : sons)
		if (dp[i][1] || dp[i][2]) vec.push_back(i);
		else {
			if (lst != -1) ans.emplace_back(lst, i), lst = -1;
			else lst = i;
			getans(i, now, 0);
		}
	if (lst != -1) ans.emplace_back(lst, getans(vec.back(), now, dp[vec.back()][1])), vec.pop_back();
	for (int i : vec)
		if (dp[i][1]) ans.emplace_back(now, getans(i, now, 1));
		else ans.emplace_back(now, getans(i, now, 2));
	return;
}

int main() {
	scanf("%d", &T);
	while (T--) {
		scanf("%d", &n);
		g.clear(n + 5);
		for (int i = 1; i < n; i++) {
			int u, v;
			scanf("%d%d", &u, &v);
			g.add(u, v), g.add(v, u);
		}
		dfs(1, 0);
		if (!dp[1][0]) {puts("-1"); continue;}
		ans.clear();
		getans(1, 0, 0);
		printf("%d\n", (int)ans.size());
		for (auto i : ans) printf("%d %d\n", i.first, i.second);
	}
	return 0;
}