#include <bits/stdc++.h>
#define rep(i,x,y) for(int i = x; i <= y; i++)
#define mid ((l + r) >> 1)
#define lch (rt << 1)
#define rch (rt << 1 | 1)

using namespace std;

using u32 = unsigned;
using i64 = long long;
using u64 = unsigned long long;

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

    vector<vector<int>> adj(n);
    rep(i,0,n-2) {
        int u, v;
        cin >> u >> v;
        u--, v--;

        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    vector<pair<int, int>> ans;
    vector<int> f(n, -1), dep(n);

    auto dfs = [&](auto& self, int x, int fa) -> void {
        if (fa != -1) {
            adj[x].erase(find(adj[x].begin(), adj[x].end(), fa));
        }
        for (auto v : adj[x]) {
            dep[v] = dep[x] + 1;
            self(self, v, x);
        }
        sort(adj[x].begin(), adj[x].end(),
            [&](int i, int j) {
                return f[i] < f[j];
            }
        );

        for (auto v : adj[x]) {
            int d = f[v] == -1 ? v : f[v];
            if (x == 0) {
                if (f[v] == -1 || f[x] == -1 || dep[f[x]] == dep[x] + 1) {
                    if (f[x] == -1) {
                        f[x] = d;
                    } else {
                        ans.emplace_back(f[x], d);
                        f[x] = -1;
                    }
                } else {
                    ans.emplace_back(x, d);
                }
            } else {
                if (f[v] == -1 || f[x] == -1) {
                    if (f[x] == -1) {
                        f[x] = d;
                    } else {
                        ans.emplace_back(f[x], d);
                        f[x] = -1;
                    }
                } else {
                    ans.emplace_back(x, d);
                }
            }
        }
    };
    dfs(dfs, 0, -1);
    if (f[0] != -1 && dep[f[0]] == 1) {
        cout << -1 << '\n';
        return;
    }
    if (f[0] != -1) {
        ans.emplace_back(0, f[0]);
    }
    cout << ans.size() << '\n';
    for (auto [u, v] : ans) {
        cout << u + 1 << ' ' << v + 1 << '\n';
    }
}

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

    int T;
    cin >> T;
    while (T--) {
        solve();
    }

    return 0;
}