I spent far more time than I intended on this but one thing lead to another and I got caught up in painting berries, adding twiggy little branches and general overall tweaking. Oddly, the berries turned out to be the biggest challenge. I mixed a combo of pyrrol red and perm. yellow for the orange. Pyrrol red, if you haven't tried it yet, is a potent color and it completely overtook the perm. yellow on the gesso. I waited until the first application of paint was dry, then gently lifted out the berries with a damp brush. The perm. yellow held onto the gesso and the pyrrol red stained just enough to create the shade of orange I was shooting for. I used some of the color mixture from the trunks to add shading and depth to the berry clusters. I created the twigs with the pointed tip of a bamboo skewer soaked in water, then dipped in undiluted tube paint.
Btw, the mystery tree with the berry clusters is a form of Mountain ash.