#include <map>
#include <vector>
#include <iostream>

int main() {
    std::map<int, std::vector<int>> tree{
        {1, {0}}, {2, {1, 0}}, {3, {2, 1, 0}}, {4, { 3, 2, 1, 0 }}, {5, { 0 }}
    };

    for (auto const &kv : tree) {
        std::cout << kv.first << " =>";
        for (auto const &i : kv.second)
            std::cout << " " << i;
        std::cout << std::endl;
    }

    return 0;
}