Yesterday I played around with NVDA and Orca for a few hours and made many tweaks and got the comment tree working.
There is a new heading - "Comments" delineating the end of a post and the start of the comments, which you can jump to.
Also I removed the markdown editor which was disrupting the tab order.
Maybe screen reader support for tree view is not very consistent and headings will turn out better. It seemed ok in NVDA.