I know there is a similar issue in the que, but this seems to have a different error, and this is for the dev version. As soon as the format is changed to tree and the main and parent fields are set to anything other than nid and saved, the following pops up. this is with and without ajax selected on the view.

An AJAX HTTP request terminated abnormally.
Debugging information follows.
Path: /admin/structure/views/view/views_models/preview/page_4/ajax
StatusText: error
ResponseText:
ReadyState: 0