Start by finding a couple more painted tree passages that you like, and copying them until the technical demands are in your grasp. Next, look for a landscape photo that includes trees, and decide how you'd like to treat them: hard edges, soft edges, or both? Value range? Color? Composition? Don't forget to consider the role the trees play in the big picture. You may decide to change some aspects of them to better support the feeling you're after.
If you find that one variable or another keeps giving you trouble, devote some time and some decent paper to practicing that.
Here are a few image that may appeal to you: