[eluser]WanWizard[/eluser]
Ah, that root_id.
You only need that if you intend to store multiple trees in the same table (like for example menu structures), in which case you use the root_id (or whatever you named it) to select the tree you want. If you don't have multiple trees, you don't need that column (or the select_root() method call).
Sorry, I don't have any code examples for you, don't have any CI running anymore since 2010.
Yes, that seems to be the correct sequence of method calls.