You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: _1028_recover_a_tree_from_preorder_traversal.rs
    path of file: ./repos/rustgym/leetcode/src/d10
    
    the code of the file until where you have to start completion: struct Solution;
use rustgym_util::*;
use std::iter::Peekable;
use std::str::Chars;
use std::vec::IntoIter;

enum Tok {
    N(i32),
    D(usize),
}

trait Preorder {
    fn parse(it: &mut Peekable<IntoIter<Tok>>, depth: usize) -> TreeLink;
    fn parse_root(it: &mut Peekable<IntoIter<Tok>>) -> TreeLink;
}

impl Preorder for
    
    fn parse(it: &mut Peekable<IntoIter<Tok>>, depth: usize) -> TreeLink {
        if let Some(&Tok::D(d)) = it.peek() {
            if d == depth {
                it.next();
                if let Some(Tok::N(n)) = it.next() {
                    TreeLink::branch(n, TreeLink::parse(it, d + 1), TreeLink::parse(it, d + 1))
                } else {
                    None
                }
            } else {
                None
            }
        } else {
            None
        }
    }