#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;
using LL = long long;

int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    int T;
    cin >> T;
    while(T--){
        int n;
        cin >> n;
        vector<vector<int> > g(n + 1);
        for(int i = 0; i < n - 1; i++){
            int a, b;
            cin >> a >> b;
            g[a].push_back(b);
            g[b].push_back(a);
        }
        int root = 1;
        while(g[root].size() > 1) root++;

        vector<pair<int, int> > ans;

        auto dfs = [&](auto &&dfs, int u, int fa) -> int {
            vector<int> son1, son2;
            for(auto j : g[u]){
                if (j == fa) continue;
                int t = dfs(dfs, j, u);
                if (t == j) son1.push_back(t);
                else son2.push_back(t);
            }
            while(son1.size() >= 2){
                int t1 = son1.back();
                son1.pop_back();
                int t2 = son1.back();
                son1.pop_back();
                ans.push_back({t1, t2});
            }
            if ((son1.size() + son2.size()) % 2 == 1){
                while(!son1.empty()){
                    son2.push_back(son1.back());
                    son1.pop_back();
                }
                while(son2.size() >= 2){
                    int t1 = son2.back();
                    son2.pop_back();
                    int t2 = son2.back();
                    son2.pop_back();
                    ans.push_back({t1, t2});
                }
                return son2[0];
            }
            if (son1.empty() and son2.empty()){
                return u;
            }
            int ret = -1;
            if (!son1.empty()){
                ret = son1[0];
                son2.push_back(u);
            }
            else{
                ret = son2.back();
                son2.pop_back();
                son2.push_back(u);
            }
            while(son2.size() >= 2){
                int t1 = son2.back();
                son2.pop_back();
                int t2 = son2.back();
                son2.pop_back();
                ans.push_back({t1, t2});
            }
            return ret;
        };

        int t = dfs(dfs, root, -1);
        if (t == g[root][0]) cout << -1 << '\n';
        else{
            ans.push_back({t, root});
            cout << ans.size() << '\n';
            for(auto [x, y] : ans){
                cout << x << ' ' << y << '\n';
            }
        }
    }

}