docs: protected void layout(TreeNode node) {
      if (node != null) {
        TreeNode child = node.child;
  
        while (child != null) {
          layout(child);
          child = child.next;
        }
  
        if (node.child != null) {
          attachParent(node, join(node));
        } else {
          layoutLeaf(node);
        }
      }
    }