#include <iostream>
#include <vector>
#include <functional>
#include <numeric>
#include <algorithm>
using namespace std;

void slove(){
    int n;
    cin >> n;

    vector<vector<int>> data(n + 1);
    vector<pair<int,int>> res;
    vector<int> node(n + 1);

    for (int i = 1 , u , v; i < n ; i++){
        cin >> u >> v;
        data[u].push_back(v);
        data[v].push_back(u);
    }
    iota(node.begin() , node.end() , 0);
    
    function<void(int,int)> dfs = [&](int ptr , int fa){
       
        for (auto nx : data[ptr]) {
          if (nx == fa) continue;
          dfs(nx , ptr);
        }

       sort(data[ptr].begin() , data[ptr].end() , [&](int i , int j){
           if (node[i] != i && node[j] != j) return i < j;
           else if (node[i] != i) return false;
           else if (node[j] != j) return true;
           return i < j;
       });

       int pre = 0;
       for (auto nx : data[ptr]){
           if (nx == fa) continue;

           if (pre == 0) pre = nx;
           else {
              res.emplace_back(node[nx] , node[pre]);
              pre = 0;
           }
       }

       if (pre) {
          if (ptr == 1 && node[pre] != pre) res.emplace_back(1 , node[pre]);
          else node[ptr] = node[pre];
       }
       return ;
    };
    
    for (int i = 1 ; i <= n ; i++){
        if (data[i].size() % 2 == 0) {
            dfs(i , -1);
            cout << res.size() << "\n";
            for (auto& val : res) {
                cout << val.first << " " << val.second << "\n";
            }
            return;
        }
    }



    cout << -1 << "\n";
    return ;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int cnt;
    cin >> cnt;

    while(cnt--){
        slove();
    }

}

/*
3
4
1 2
2 3
2 4
7
1 2
1 3
1 4
4 5
4 6
4 7
6
1 2
2 3
2 4
1 5
5 6
*/