[nmsmith]

> building a tree in Rust will do a lot of reference counting

This isn't true in most cases. If every subtree is only referenced by its (unique) parent, then you can use a standard Rust "Box", which means that during compilation, the compiler inserts calls to malloc() (when the Box is created) and free() (when the Box goes out of scope). There will be no reference counting — or any other overhead — at runtime.

[pjmlp]

Tree based structures with root ownership are very constrained as general purpose data structure.