#include <bits/stdc++.h>

using namespace std;

typedef long long i64;
typedef unsigned long long u64;
typedef double lf;

vector< vector<int> > tree;
vector< pair<int, int> > edges;

pair<int, int> dfs(int v, int p) {
    vector< pair<int, int> > children;
    for (int u : tree[v]) {
        if (u == p) continue;
        children.push_back(dfs(u, v));
        // cerr << "ret from " << u + 1 << " " << children.back().first << ' ' << children.back().second + 1 << endl;
    }
    sort(children.begin(), children.end());
    if (children.size() % 2 == 0) {
        if (!children.empty() && children.back().first > 1 && p != -1) {
            for (int i = 0; i + 2 < (int) children.size(); i += 2) {
               edges.push_back({children[i].second, children[i + 1].second});
            }
            edges.push_back({children.back().second, v});
            int idx = (int) children.size() - 2;
            return {children[idx].first + 1, children[idx].second};
        } else {
            for (int i = 0; i + 1 < (int) children.size(); i += 2) {
               edges.push_back({children[i].second, children[i + 1].second});
            }
            return {1, v};
        }
    }

    for (int i = 0; i + 1 < (int) children.size(); i += 2) {
        edges.push_back({children[i].second, children[i + 1].second});
    }
    
    if (p == -1) {
        if (children.back().first == 1) {
            return {-1, -1};
        }
        else {
            edges.emplace_back(children.back().second, v);
        }
    } 
    return {children.back().first + 1, children.back().second};
}

const auto ROOT = 1488300228;

void solve() {
    int n;
    cin >> n;
    tree.assign(n, vector<int>());
    for (int i = 1; i < n; i++) {
        int a, b;
        cin >> a >> b;
        --a, --b;
        tree[a].push_back(b);
        tree[b].push_back(a);
    }
    edges.clear();

    // cerr << "ROOT = " << ROOT % n + 1 << endl;
    if (dfs(ROOT % n, -1).first == -1) {
        cout << "-1\n";
    } else {
        cout << edges.size() << '\n';
        for (auto [a, b] : edges) {
            cout << a + 1 << ' ' << b + 1 << '\n';
        }
    }
}

signed main() {
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
#endif
    ios_base::sync_with_stdio(false);
    int t = 1;
    cin >> t;
    for (int i = 0; i < t; i++) {
        solve();
    }
}