Personally, I never liked the realistic style very much.

For top down trees you could look into Larb and Lingon work for inspiration
http://www.cartographersguild.com/fi...o-village.html
http://www.cartographersguild.com/at...-10-72dpi-.jpg

A good tuto if you like the style: http://www.cartographersguild.com/tu...-tutorial.html