show entire Book Navigation tree
It turns that I already posted the answer in the question, but somehow missed it during testing!

Removing , $node-&gt;book from $tree = $this-&gt;bookManager-&gt;bookTreeAllData($node-&gt;book['bid'], $node-&gt;book); does print the entire expanded tree.

If someone has time to add a user form option to the module it could eventually benefit many and get on the drupal.org repo.