When painting a tree, the trunk and leaves are the foundation of your painting. Painting the bark is more than just a layer of brown paint on your tree. To get a realistic painting of a tree trunk, use different colours, shades, and techniques.
Paint your trunk or branches using a medium tip paint brush and brown paint. Apply two coats.
Mix a brown paint and a red paint together on a palette. The result should be a brown with hints of red. Apply this paint with a small, rounded tip paintbrush in small, rounded strokes. Apply this colour to the entire tree without getting entire coverage. You want the original colour to peek through.
Add a small amount of white to the red and brown mixed paint. Start at the edges of your trunk and branches. The strokes should not go all the way across the trunk or branch. This will create a highlighted area on your branches. Continue to add more white and adding paint until you are satisfied with the highlights.
Paint shadows on the bark. In areas of your painting that you want to bark to look like it is in a shadow, paint an extra coat of the original dark brown paint.
Paint white edges on some of your branches to create additional highlights on your branch.
Keep brush strokes light and rounded. Do not attempt to fill in the entire branch with one colour; the varying colours creates the look of the branch. Highlights should not be at regular intervals; real bark is more randomly spaced.