#include<bits/stdc++.h>
using namespace std;
const int maxn = 300005;
int T, n, fl = 1;
vector<int> a[maxn];
int f[maxn], dep[maxn];
vector<pair<int, int> > ans;
void dfs(int fa, int x) {
    dep[x] = dep[fa] + 1;
    vector<int> vec;
    for (int i = 0; i < a[x].size(); i++) {
        int y = a[x][i];
        if (y == fa) continue;
        dfs(x, y);
        vec.emplace_back(f[y]);
    }
    std::sort(vec.begin(), vec.end(), [&] (int i, int j) { return dep[i] > dep[j]; });
    if (vec.size() % 2 == 0) {
        if (x == 1) {
            f[x] = x;
            for (int i = 0; i < vec.size(); i += 2) ans.emplace_back(vec[i], vec[i + 1]);
            return;
        }
        if (!vec.size()) {
            f[x] = x;
        } else {
            for (int i = 2; i < vec.size(); i += 2) ans.emplace_back(vec[i], vec[i + 1]);
            if (dep[vec[1]] > dep[x] + 1) ans.emplace_back(x, vec[1]), f[x] = vec[0];
            else if (dep[vec[0]] > dep[x] + 1) ans.emplace_back(x, vec[0]), f[x] = vec[1];
            else f[x] = x, ans.emplace_back(vec[0], vec[1]);
        }
    } else {
        f[x] = vec[0];
        for (int i = 1; i < vec.size(); i += 2) ans.emplace_back(vec[i], vec[i + 1]);
    }
}
void work() {
    cin >> n; ans.clear();
    for (int i = 1; i <= n; i++) a[i].clear();
    for (int i = 1; i < n; i++) {
        int x, y; cin >> x >> y;
        a[x].push_back(y), a[y].push_back(x);
    }
    fl = 1;
    dfs(0, 1);
    if (dep[f[1]] == 2) {cout << -1 << '\n'; return;}
    if (f[1] != 1) ans.emplace_back(1, f[1]);
    cout << ans.size() << '\n';
    for (auto p : ans) cout << p.first << ' ' << p.second << '\n';
}
int main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    cin >> T;
    while (T--) work();
    return 0;
}