Is is a bit old, but ...
On a Mac, hold down the Command key and click the black triangle next to any entry in the list. I assume it works the same in Windows with the Control key, but i have no way to confirm that.
I hope that helps.
Didn't you read my text? I wrote: "Command+Click opens only the first level".
Use the Mac-equivalents of these key combinations:
click: expand the selected topic one level down
Alt+click: expand selected topic to show all subtopics
Alt+Ctrl+click: expand all topics, show only first level of all topics.
It's not possible to expand all levels of all topics with one (modified) click or with a script.
Peter, thank you. Yes, I did know these shortcuts but was indeed searching for expansion of all levels including all sublevels ...