I found this great program for the iPad called ‘TreeSketch 3.0’ in the app store the other day. It is a free download and the program is able to create great looking trees with just a few hand jestures. It is very intuitive as I could use it directly after download without watching any of the tutorials which are quite good so if you are inclined to, download this app and give it a try. I found a few comments regarding individuals having problems with the app with regard to uploading to dropbox but I found no problems. Once uploaded you can import the tree into blender as a .obj. When imported you have materials setup for the leaves and branches, diffuse color is white so you need to change that and you are good to go for a tree in your scene. As imported they are perfect for distance placement however for close up you will need to add textures to the branches and leaves and this program makes this easy. The .zip file uploaded into dropbox also contains the .png textures for the leaves and bark plus a hires transparent .png for use.
I recommend giving this program a shot as it is fantastic especially for a free program.
(I’ll upload a tree this afternoon when I am home)