I don’t, and it’s nothing to do with “tree form” (I use GMail’s web interface, so I don’t see email in tree form, either - linear form is not new to me and I have a well-developed workflow for linear conversations. It’s to do with “if I scroll back up to read something earlier, I lose my place”.
When the thread is long and you have unread messages you have a back button on the scroll bar. I don’t know exactly the details of this element (or if we need to activate it somehow) but the feature exists. Is this more or less what you were searching for?
