#include <bits/stdc++.h>
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define F(i, x, y) for (int i = (x); i <= (y); i++)
#define R(i, x, y) for (int i = (x); i >= (y); i--)
#define FIO(FILE) freopen(FILE".in", "r", stdin), freopen(FILE".out", "w", stdout)

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
bool Mbe;

const int N = 3e5 + 5;

int n, rt, flg, p, q, a, b;
int sz[N], f[N], s[N][2], vs[N];

vector<int> G[N];
vector<pi> res;

void dfs1(int u, int fa) {
	sz[u] = 1, f[u] = fa;
	s[u][0] = s[u][1] = 0;
	for (int v : G[u]) {
		if (v == fa) {
			continue;
		}
		dfs1(v, u);
		sz[u] += sz[v];
		if (sz[v] & 1) {
			if (s[u][0]) {
				s[u][1] = v;
			} else {
				s[u][0] = v;
			}
		}
	}
	if (s[u][0]) {
		for (int v : G[u]) {
			if (v == fa || (sz[v] & 1)) {
				continue;
			}
			if (s[v][0]) {
				if (s[u][0] != v && ((n - sz[s[u][0]] - sz[v]) & 1)) {
					flg = 2;
					q = u, p = s[u][0], a = v, b = s[v][0];
				}
				if (s[u][1] && s[u][1] != v && ((n - sz[s[u][1]] - sz[v]) & 1)) {
					flg = 2;
					q = u, p = s[u][1], a = v, b = s[v][0];
				}
			}
		}
	}
}

bool dfs2(int u, int fa) {
	vector<int> p;
	for (int v : G[u]) {
		if (v == fa || vs[v]) {
			continue;
		}
		if (dfs2(v, u)) {
			p.eb(v);
		}
	}
	int fl = 1;
	if ((int)p.size() & 1) {
		assert(fa != 0);
		res.eb(fa, p.back()), p.pop_back(), fl = 0;
	}
	while (!p.empty()) {
		int v1 = p.back(); p.pop_back();
		int v2 = p.back(); p.pop_back();
		res.eb(v1, v2);
	}
	return fl;
}

void out() {
	cout << res.size() << '\n';
	for (pi p : res) {
		cout << p.fi << ' ' << p.se << '\n';
	}
	res.clear();
}

void solve() {
	cin >> n;
	F (i, 1, n) {
		vs[i] = 0;
		G[i].clear();
	}
	F (i, 1, n - 1) {
		int u, v;
		cin >> u >> v;
		G[u].eb(v), G[v].eb(u);
	}
	if (n & 1) {
		dfs2(1, 0);
		out();
		return;
	} else {
		flg = 0;
		dfs1(1, 0);
		F (u, 1, n) {
			if (f[f[f[u]]] && (sz[u] & 1) && !(sz[f[u]] & 1) && (sz[f[f[u]]] & 1) && ((n - sz[f[f[u]]]) & 1)) {
				flg = 1, rt = u;
			}	
		}
		if (!flg) {
			cout << -1 << '\n';
			return;
		}
		if (flg == 1) {
			vs[rt] = vs[f[rt]] = vs[f[f[rt]]] = vs[f[f[f[rt]]]] = 1;
			dfs2(rt, 0);
			dfs2(f[rt], 0);
			dfs2(f[f[rt]], 0);
			dfs2(f[f[f[rt]]], 0);
			res.eb(rt, f[f[f[rt]]]);
		} else {
			vs[p] = vs[q] = vs[a] = vs[b] = 1;
			dfs2(p, 0);
			dfs2(q, 0);
			dfs2(a, 0);
			dfs2(b, 0);
			res.eb(p, b);
		}
		out();
	}
}

bool Med;
int main() {
	// FIO("");
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	cerr << (&Mbe - &Med) / 1048576.0 << " MB\n";
	int T = 1;
	cin >> T;
	while (T--) solve();
	cerr << (int)(1e3 * clock() / CLOCKS_PER_SEC) << " ms\n";
	return 0;
}