... the protection feature that warns you that you're closing the app without saving the tree sometimes forgets to warn you.
let me fix this, and then decide whether auto saving tree changes should be automatic.
In practice, one does more saving than aborting of changes, so in this sense, auto saving trees and variables on program exit makes sense. I have an accounting program (Simply Accounting by ACTPAC, excellent product) that works by auto saving. At first I was concerned, but as long as the File > Revert option is available, it hasn't been a problem, and I have never lost a thing. I rarely even open the File menu on my accounting program.
There is an issue that when you switch trees, you'll need to auto save on the switch. That means if you switch back to the original tree and want to revert, you can't (unless the program saves *.bak files for trees). However, I'm using several tree files and I've never experienced a case where I wanted to do that. And with the present implementation, doing this maneuver would still be a problem.