Tree Retrieval

There is a hidden tree with $N$ vertices labeled $1, 2, \ldots, N$. Your task is to recover the edges of the tree. You can ask queries, where you give a set $S$ of size **at least** $2$ to the judge. - Call a vertex $x \in S$ isolable, if there exists an edge in the tree such that if we remove this edge, no other vertex $y \in S$ is reachable from $x$. - The judge returns two integers, the fir