fn traverse_tree(tree: &Tree, vec: BitVec) -> HashMap<u8, BitVec> {
    match tree.data {
        Some(byte) => {
            let mut map = HashMap::with_capacity(1);
            map.insert(byte, vec);
            map
        }
        None => {
            let mut left_vec = vec.clone();
            left_vec.push(false);
            let mut right_vec = vec.clone();
            right_vec.push(true);
            let left_map = traverse_tree(tree.left.unwrap().as_ref(), left_vec);
            let right_map = traverse_tree(tree.right.unwrap().as_ref(), right_vec);
            let mut map = HashMap::with_capacity(left_map.len() + right_map.len());
            map.extend(left_map);
            map.extend(right_map);
            map
        }
    }
}