Another approach to creating the illusion of form in painting is through brushwork. Here you can see how Pissarro, Van Gogh and Cezanne approached painting trees.
The effect of superimposing different dabs of green in the top painting gives it a heightened sense of light while the flowing directional lines provide a strong rhythm in Van Gough's Cypress. In the bottom painting the unidirectional "constructive brushwork" is a precursor of cubism and provides a sense of solidity to the forms.
We still have to think about blocking our forms so that we can simplify the shapes and choose colours according to their value so as to keep our composition under control. We will see what we can do with and analogue palette of blues and greens. Above all we have to find ways of avoiding painting leaves!