#include <bits/stdc++.h>
using namespace std;
#define int long long

std::vector<std::pair<int, int>> ans;
int len;
int rt;
int tmprt;
std::pair<int, int> dfs(std::vector<std::vector<int>>& e, int u, int fa) {
    int cnt = 0;
    std::vector<std::pair<int, int>> res;
    std::pair<int, int> PII = {1, u};
    for (auto& v : e[u]) {
        if (v == fa) continue;
        res.push_back(dfs(e, v, u));
    }
    std::sort(res.begin(), res.end());
    for (int i = 1; i < res.size(); i += 2) {
        ans.emplace_back(res[i - 1].second, res[i].second);
    }
    if (u == rt) {
        if (res.size() & 1) {
            len = res.back().first;
            ans.emplace_back(rt, res.back().second);
        } else
            len = 100;
        return PII;
    }
    if (res.size() & 1) {
        PII.first = res.back().first + 1;
        PII.second = res.back().second;
        if(!tmprt&&PII.first>1)
        {
            tmprt=u;
        }
    }
    else
    {
      if(!tmprt&&!res.empty()&&res.back().first>1) tmprt=res.back().second;

    }
    if(e[u].size()%2==1&&!tmprt) tmprt=u;
    return PII;
}

/*
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
*/
int curt,ptt;

void  bianli(std::vector<std::vector<int>>& e,int root,int fa)
{
    printf("%d %d\n",root,fa);
    for(auto x:e[root])
    {
       if(x==fa) continue;
       bianli(e,x,root);
    }

}
int in[2000009];

void solve() {
    curt++;
    len = 0;
    rt=0;
    tmprt=0;
    ans.clear();
    int n;
    std::cin >> n;
    std::vector<std::vector<int>> e(n + 1);

    for (int i = 0; i < n - 1; i++) {
        int a, b;
        std::cin >> a >> b;
        in[a]++;in[b]++;
        e[a].emplace_back(b);
        e[b].emplace_back(a);
    }
    // if(ptt==60000&&curt==33)
     //{
      //  printf("WAWWAWAWWAWA:%d\n",n);
      //  bianli(e,1,1);
     //}
      for(int i=1;i<=n;i++)
      {
         if(in[i]%2==0)
         {
            rt=i;
            break;
         }

      }
      for(int i=1;i<=n;i++) in[i]=0;
     //rt=1;
     if(rt)
    dfs(e, rt, rt);
    if(rt)
    {
       cout << ans.size() << "\n";
              for (auto [a, b] : ans) {
            cout << a << " " << b << "\n";
    }
    }
    else
    {
        cout<<"-1 "<<endl;
    }
    // std::cout << len << ' ';

}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int t = 1;
    std::cin >> t;
    ptt=t;
    for (int i = 0; i < t; ++i) {
        solve();
    }

    return 0;
}

/*
10
10
1 2
1 3
1 4
2 5
2 6
3 7
3 8
4 9 4
10
*/