It's append only until B and C get a copy and each append their own comments, then D and E get two separate forks and append their own comments. That can work f

It's append only until B and C get a copy and each append their own comments, then D and E get two separate forks and append their own comments. That can work for trees to which you only append, such as comments. That does NOT work for any operations that do non-append operations on trees, such as operations which rearrange the tree into a line. So yes, for append-only tree structures, this may work. In terms, of say, a Google Doc that means you can never delete or insert any text, but only append text to the end of paragraphs etc. Certainly very limiting. Unless there's something you haven't described, in which case I encourage you to provide a more in-depth comment describing a solution for actually inserting or modifying the tree.