This is a reference photograph, not to copy exactly but to help with understanding the colour and form of the tree. The best thing to do is get outdoors and find some trees and make drawings and paintings from life after you have had a bit of practice with some colour mixing and techniques. This is what we are doing at the moment in the classes at Gelli Aur.
Sometimes it works well to first draw the outline of a tree and then put a soft wet into wet wash behind it before painting detail on the tree. It is best to wet the area first with clean water before dropping in the colour. Remember to mix up lots of colour first to the right concentrations of pigment and water.
There are some examples of quick studies done this way below. In my next post I shall give some tips for painting the bark of birches and techniques that can also be applied to other types of trees.