// author : thembululquaUwU
// 3.9.2024

#include <bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
#define endl '\n'

using namespace std;
using ll = long long;
using ii = pair <int, int>;
using vi = vector <int>;

const int MaxN = 2e5;
const int mod = 1e9 + 7;

void maxl(auto &a, auto b) {a = max(a, b);}
void minl(auto &a, auto b) {a = min(a, b);}

template <class Fun> class y_combinator_result { Fun fun_; public: template <class T> explicit y_combinator_result(T &&fun): fun_(forward<T>(fun)) {} template <class...Args> decltype(auto)operator()(Args &&...args) { return fun_(ref(*this), forward<Args>(args)...); } };
template <class Fun> decltype(auto)y_combinator(Fun &&fun) { return y_combinator_result<decay_t<Fun>>(forward<Fun>(fun)); }

void solve(){
    int n; cin >> n;
    vector <vi> adj(n);
    for (int i = 1, u, v; i < n; ++ i){
        cin >> u >> v;
        -- u, -- v;
        adj[u].pb(v); adj[v].pb(u);
    }

    if (n == 2){
        cout << -1 << endl;
        return;
    }

    int root = 0;
    for (int i = 0; i < n; ++ i){
        if (adj[i].size() == 1)
            root = i;
    }

    vector <int> up(n, -1);
    vector <pair <int, int>> ans;
    bool ok = 1;
    auto dfs = y_combinator([&](auto dfs, int u, int p) -> void {
        up[u] = u;
        int nchild = 0, can_match = -1;
        for (int v : adj[u]) if (v != p){
            dfs(v, u);
            nchild ++;
            if (up[v] != v) can_match = up[v];
        }

        if (u == root && can_match < 0){
            cout << -1 << endl;
            ok = 0;
            return;
        }

        if (u == root){
            ans.push_back({u, can_match});
            return;
        }

        if (nchild % 2 == 1 || can_match < 0){
            int last = -1;
            for (int v : adj[u]) if (v != p){
                if (last < 0) last = up[v];
                else {
                    ans.push_back({last, up[v]});
                    last = -1;
                }
            }

            up[u] = last;
            if (up[u] < 0) up[u] = u;
        }

        else {
            ans.push_back({u, can_match});
            int last = -1;
            for (int v : adj[u]) if (v != p && up[v] != can_match){
                if (last < 0) last = up[v];
                else {
                    ans.push_back({last, up[v]});
                    last = -1;
                }
            }

            up[u] = last;
            if (up[u] < 0) up[u] = u;
        }


    });

    dfs(root, -1);
    if (!ok) return;
    cout << ans.size() << endl;
    for (auto [x, y] : ans) cout << x + 1 << ' ' << y + 1 << endl;
}

int main(){
    if (fopen("pqh.inp", "r")){
        freopen("pqh.inp", "r", stdin);
        freopen("pqh.out", "w", stdout);
    }
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    int t = 1; cin >> t;
    while (t --) solve();
    return 0;
}