i am a little down today

...and here is why,,,for the longest i have been wanting to paint like Bob Ross with my gimp....and for those who don't know who he is, here is a small video showing you who i am talking about...
http://www.youtube.com/watch?v=MghiBW3r65MBob Ross painted with oil paints and a canvas. now i have done some paintings very similar to this type of painting he does with my gimp, but i cannot seem to find the right brush to do the trees or bushes with....i have tried my best to make my own brush, but can't seem to find that one that works just right...here is a picture of a painting that i did with gimp, and you can see how awful the trees look.....i am very happy with my mountains but not so happy with my trees...
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i am doing my best to find a way to paint trees and bushes but i do not want a brush that already has the tree already shaped..if you know what i am getting at. to me that is not painting.... here is another one i have done and i have been learning to do the water a little better...but i wanted to add some trees to this picture but because i am so bad with trees i left them out...
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i just wished someone on here could help me find the right brush or technique to get the result i want...maybe what i want is impossible...but i hope i am wrong to assume that...anyways any help from you guys will be appreciated. like i said i am not looking for a brush to where the tree is already made for me...and i guess what i am really looking for is a brush or technique that will help me paint the leaves on the trees with...