This arena tree structure is using just a single Vec and numerical identifiers (indices in the vector) instead of reference counted pointers. This means there is no RefCell and mutability is handled in a way much more idiomatic to Rust through unique (&mut) access to the arena. The tree can be sent or shared across threads like a Vec. This enables general multiprocessing support like parallel tree traversals.

use indextree::Arena;

// Create a new arena
let arena = &mut Arena::new();

// Add some new nodes to the arena
let a = arena.new_node(1);
let b = arena.new_node(2);

// Append a to b
assert!(a.append(b, arena).is_ok());
assert_eq!(b.ancestors(arena).into_iter().count(), 2);

https://github.com/mooman219/generational_arena_bench