Very similar to the stones & aligned objects editor. This allows you to easily reorganize you tree's menu in the editor while your working, move the tree's around in the sections, delete any you don't like and then some more.
Have a quick look here:
Point to note: You cannot actually set up a new section and add objects from within this editor, this is done in the .rsr file and define the name in a text file ( nations.txt: #SECTIONNAME Display Name).
Also, after exiting the game and reloading it will load up the default .rsr sections. However any maps made with changes to trees and saved, will still display these changes after restarting the game.
The main usage of this editor is to visually fine tune the various coordinates for the objects without having to load up the game constantly. Once you get it right, write down the settings in the .rsr and .lst file.
Notice how it doesn't matter if there are stone's or trees in the treeseditor, it's just what is in the .g17 files that matters. As long as you define the appropriate resource in the .rsr file.
Also, i renamed all the weird name's they had. For example this menu says "Stone Mine's"
This is done by simply adding the existing line #STONESTOEXTRACT to Text\nations.txt and then add a description behind it. Some are pretty clear like this one, but there's a whole list and when i see name's like paporotnik , sosna, el,...i really dont know what it is without actually opening up the menu.