Got it give me a sec.
http://www.englanddesign.com/quilt-g.../Open%20Season
In case you hadn't heard of her, Cynthia did this amazing quilt (among others) - This one won at Houston. It's all paper pieced.
I think this is the method you want.
Check out her getting started page/videos for her method - she calls it Picture Piecing:
http://www.englanddesign.com/content/video-demos-0
You don't have to go as teeny tiny as she does, but you can still get a lot of detail and definition into the image.
And you can further embellish it with the quilting or embroidery or whatever method you want.
Also, when you're shaping the tree, most of the detail of the thinner branches can be done with thread - you don't have to actually pp those small parts.