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

void solve() {
    int n; cin >> n;
    vector<vector<int>> G(n + 1);
    vector<int> deg(n + 1);
    for (int i = 1;i < n;i++) {
        int u, v; cin >> u >> v;
        deg[u]++, deg[v]++;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    int ok = 0;
    for (int i = 1;i <= n;i++) {
        if (deg[i] % 2 == 0) {
            ok = i;
            break;
        }
    }
    if (!ok) {
        cout << -1 << '\n';
        return;
    }
    int pre = 0;
    vector<int> vis(n + 1, 0), F(n + 1, 0);
    map<int, int> mp;
    auto dfs = [&](auto&&dfs, int u, int fa) -> void {
        vector<int> tmp;
        for (int v : G[u]) {
            if (v != fa) {
                tmp.push_back(v); 
                F[v] = u;
                dfs(dfs, v, u);
            }
        }
        int m = tmp.size();
        for (int i = 1;i < m;i += 2) {
            int a = tmp[i], b = tmp[i - 1];
            vis[a] = 1, vis[b] = 1;
            mp[a] = b;
            mp[b] = a;
        }
    };
    dfs(dfs, ok, ok);
    // cout << "root: " << ok << '\n';  
    // for (int i = 1;i <= n;i++) cout << i << ": " << vis[i] << '\n';
    auto dfs1 = [&](auto&&dfs1, int u, int fa) -> void {
        for (int v : G[u]) {
            // cout << "v: " << v << '\n';
            if (v == fa) continue;
            if (!vis[v]) {
                int rhs = mp[u];
                mp.erase(u);
                mp[v] = rhs;
                mp[rhs] = v;
                vis[v] = 1;
            }
            dfs1(dfs1, v, u);
        }
    };
    dfs1(dfs1, ok, ok);

    vector<int> tag(n + 1);
    vector<pair<int, int>> ans;
    for (auto& [u, v] : mp) {
        if (tag[u] || tag[v] || !u || !v || u == v) continue;
        // cout << u << " " << v << '\n';
        ans.push_back(make_pair(u, v));
        tag[u] = 1, tag[v] = 1;
    }
    cout << ans.size() << '\n';
    for (auto& [u, v] : ans) {
        cout << u << " " << v << '\n';
    }
}

int main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int t; cin >> t;
    while (t--) solve();
}