This was actually done as part of our 1st internals and should have been posted a few months ago.
It took me about 3 hours to do, done entirely in Photoshop (no customized brushes were used).
I think everything turned out quite well (except the treehouse looks a little too much exposed...it would have been better if it was "hidden" deeper in the tree). The staircase leading up to the treehouse is not in perspective, and I only realized this after completing the painting...The rocky shore and water were done in less than 5 minutes (as we were all given only 3 hours to complete this) and those could have been a little more refined as well.
Feedback and questions are always appreciated and encouraged!