Refs for tree nodes in rust...

let tree: Option<Box<Node>> = Some(...);

let a = &tree;
// &Option<Box<Node>>

let b = tree.as_ref();
// Option<&Box<Node>>

let c = tree.as_deref();
// Option<&Node>

also...

unwrap()               // take the thing out and own it
as_ref().unwrap()      // borrow the thing inside
as_deref().unwrap()    // borrow through Box/Rc/String/etc. to the inner target