I have not programmed Rust, yet. But this article gives me a feeling that this looks similar to database transactions. This might be wildly wrong but for me I see an analogy:
Once you get the &mut reference, you have your tree, which then looks to me like you have created a transaction. An in this transaction context you do your things.
Once you get the &mut reference, you have your tree, which then looks to me like you have created a transaction. An in this transaction context you do your things.