Kann den Knoten nicht mehr als einmal als veränderlich ausleihen, während ein binärer Suchbaum implementiert wird

Ich versuche einen binären Suchbaum in Rust zu implementieren und habe Probleme beim Einfügen eines Elements. Was ist ein idiomatischer Weg, dies in Rust zu tun?

Hier ist meine Implementierung:

use std::cmp::Ordering;

pub struct BinarySearchTree {
    root: OptNode,
    size: u32,
}

type OptNode = Option<Box<Node>>;

struct Node {
    key: i32,
    left: OptNode,
    right: OptNode,
}

impl BinarySearchTree {
    pub fn new() -> Self {
        BinarySearchTree {
            root: None,
            size: 0,
        }
    }

    pub fn is_empty(&self) -> bool {
        self.size == 0
    }

    pub fn size(&self) -> u32 {
        self.size
    }

    pub fn contains(&self, key: i32) -> bool {
        let mut node = &self.root;
        while let Some(ref boxed_node) = *node {
            match key.cmp(&boxed_node.key) {
                Ordering::Less => node = &boxed_node.left,
                Ordering::Greater => node = &boxed_node.right,
                Ordering::Equal => return true,
            }
        }

        false
    }

    pub fn insert(&mut self, key: i32) {
        let mut node = &mut self.root;
        while let Some(ref mut boxed_node) = *node {
            match key.cmp(&boxed_node.key) {
                Ordering::Less => node = &mut boxed_node.left,
                Ordering::Greater => node = &mut boxed_node.right,
                Ordering::Equal => return,
            }
        }

        *node = Some(Box::new(Node {
            key: key,
            left: None,
            right: None,
        }));
    }
}

fn main() {}

Hier sind die Fehler, die ich bekomme:

error[E0499]: cannot borrow `node.0` as mutable more than once at a time
  --> src/main.rs:47:24
   |
47 |         while let Some(ref mut boxed_node) = *node {
   |                        ^^^^^^^^^^^^^^^^^^ mutable borrow starts here in previous iteration of loop
...
60 |     }
   |     - mutable borrow ends here

error[E0506]: cannot assign to `node` because it is borrowed
  --> src/main.rs:49:35
   |
47 |         while let Some(ref mut boxed_node) = *node {
   |                        ------------------ borrow of `node` occurs here
48 |             match key.cmp(&boxed_node.key) {
49 |                 Ordering::Less => node = &mut boxed_node.left,
   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `node` occurs here

error[E0506]: cannot assign to `node` because it is borrowed
  --> src/main.rs:50:38
   |
47 |         while let Some(ref mut boxed_node) = *node {
   |                        ------------------ borrow of `node` occurs here
...
50 |                 Ordering::Greater => node = &mut boxed_node.right,
   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `node` occurs here

error[E0506]: cannot assign to `*node` because it is borrowed
  --> src/main.rs:55:9
   |
47 |           while let Some(ref mut boxed_node) = *node {
   |                          ------------------ borrow of `*node` occurs here
...
55 | /         *node = Some(Box::new(Node {
56 | |             key: key,
57 | |             left: None,
58 | |             right: None,
59 | |         }));
   | |___________^ assignment to borrowed `*node` occurs here

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