I have no school right now, and there's no tutorials on Tree Isomorphism on Codeforces, so I decided to write one :).

What is a tree isomorphism?

Maybe you recognize the word isomorphic: in the context of abstract algebra when two objects are effectively the same, but are labelled differently. We can extend this to trees as well: two trees are isomorphic if they are the same, but may have different node labels. For example,