Wow, great job writing this up!
I struggled when working with the TreeView about a month ago. I eventually figured it out, but it became clear to me that there was insufficient documentation out there to make things easy for first-time users of these widgets.
If I had only waited a month, I would have had a much easier time, I think, thanks to your excellent tutorial here.
So, thanks for this, even if I missed the chance to maximally benefit from it!