There's an app called "Autotrees Beta" that will do some automatic tree placement for you, I've used it, it sorta works, but what I've found is the quickest method is to save an arrangement of trees in Notepad, believe it or not.
The idea is to fill up an entire 256x256 tile with tiny veg rectangles, very small rectangles, as small as the annotator will allow. Spread them out and keep an eye on the lower right status bar so that you don't exceed 600 trees on a single tile. Now do the selection rectangle thing selecting all of them and press Ctrl+C, open Notepad and paste, save.
When you open the next tile to be annotated, Ctrl+A, Ctrl+C the entire Notepad document and then right click in the annotator to paste the entire tile full of trees in one whack.
At this point annotation becomes a process of deletion rather than addition. Select and delete the trees from open areas, housing, etc. You'll still have to annotate all your houses which is a pain in itself, but if you have outlying areas in your photoreal that are primarily forested the Notepad trick can save you a lot of time.
I attached a txt file that contains 599 tree placements to save you some trouble.
Jim