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

using ll = long long;
#define rep(i, n) for (ll i = 0; i < n; i++)
#define rep2(i, l, r) for (ll i = l; i < r; i++)

using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;

/* ---- */
#define all(A) A.begin(), A.end()
#define elif else if
using pii = pair<ll, ll>;

bool chmin(auto &a, const auto &b) { return a > b ? a = b, 1 : 0; }
bool chmax(auto &a, const auto &b) { return a < b ? a = b, 1 : 0; }

struct IOSetup {
  IOSetup() {
    cin.tie(0);
    ios::sync_with_stdio(0);
  }
} iosetup;

template <class T>
void print(vector<T> a) {
  for (auto x : a) cerr << x << ' ';
  cerr << endl;
}

void print(auto x) { cerr << x << endl; }

template <class Head, class... Tail>
void print(Head &&head, Tail &&...tail) {
  cerr << head << ' ';
  print(forward<Tail>(tail)...);
}

void solve(){
  int n;
  cin>>n;
  vi deg(n);
  vvi edge(n);
  rep(i,n-1){
    int u,v;
    cin>>u>>v;
    u--;v--;
    edge[u].push_back(v);
    edge[v].push_back(u);
    deg[u]++;
    deg[v]++;
  }

  bool ok=true;
  vector<pair<int,int>>ans;
  auto dfs=[&](auto dfs,int v,int p)->pair<int,int>{
    vi ok1,ok2;
    int sz=0;
    for(auto u:edge[v]){
      if(u!=p){
        pair<int,int>res=dfs(dfs,u,v);
        if(res.first!=-1){
          if(res.first==2)ok2.push_back(res.second);
          else ok1.push_back(res.second);
          sz++;
        }
      }
    }
    bool used=false;
    // print(v,ok1.size(),ok2.size());
    if(deg[v]%2==0)used=true;
    if(!used&&ok2.size()>=1){
      used=true;
      int x=ok2.back();
      ok2.pop_back();
      ans.push_back({v,x});
    }
    if(!used&&ok1.size()%2==1){
      ok=false;
      return {-1,-1};
    }
    vi rem;
    for(auto x:ok1)rem.push_back(x);
    for(auto x:ok2)rem.push_back(x);
    while(rem.size()>=2){
      int x=rem.back();
      rem.pop_back();
      int y=rem.back();
      rem.pop_back();
      ans.push_back({x,y});
    }
    if(!used){
      return {1,v};
    }
    elif(rem.size()==1){
      return {2,rem.back()};
    }
    else{
      return {-1,-1};
    }
  };

  dfs(dfs,0,-1);
  if(ok){
    cout<<ans.size()<<'\n';
    for(auto [u,v]:ans){
      cout<<u+1<<' '<<v+1<<'\n';
    }
  }
  else{
    cout<<-1<<'\n';
  }
}

int main(){
  int T;
  cin>>T;
  rep(i,T)solve();  
}