#include <bits/stdc++.h>

using namespace std;

vector<int> a;
vector< vector<int> > G, res;

void dfs(int x, int fa = 0) {
    res.back().push_back(x);
    vector<int> lf;
    for (auto v : G[x]) if (G[v].size() == 1) lf.push_back(v);
    if (a[x] ^= 1) reverse(lf.begin(), lf.end());
    for (auto v : lf) res.back().push_back(v);
    for (auto v : G[x]) if (v != fa && G[v].size() >= 2) dfs(v, x);
}

signed main() {
    int T; scanf("%d", &T);
    while (T--) {
        int n; scanf("%d", &n);
        G = vector< vector<int> >(n + 1, vector<int>()), a = vector<int>(n, 0), res.clear();
        for (int i = 1, x, y; i < n; ++i) {
            scanf("%d%d", &x, &y), G[x].push_back(y), G[y].push_back(x);
        }
        for (int i = 1; i <= n; ++i) {
            int c = 0;
            for (auto v : G[i]) c += (G[v].size()>= 2);
            if (G[i].size() >= 2 && c <= 1) {
                int t = 1 + (c == 0);
                while (t--) res.push_back({}), dfs(i);
            }
        }
        printf("%d\n", (int)res.size());
        for (auto x : res) {
            for (int i = n - 1; ~i; --i) printf("%d%c", x[i], " \n"[!i]);
        }
    }
    return 0;
}