Could you please tell us whether you want to change the size of the menu item?
Sorry, current version of Sothink Tree Menu only support using Width and Height box under Global Settings>General panel to edit the whole width and height of the menu, but not the menu items.
If you want to resize the menu item, you can do it manually by adding blank to the menu items.
Thanks a lot for your understanding. If later on we see any chance to do better, we will let you soon as soon as possible.