OK, this is a study of an oak tree trunk. I settled on using burnt umber as it's a very dark color that lightens up well into the colors I wanted. Pthalo green is the color I also chose for the leaves. I used cadmium yellow hue, some burnt umber and some titanium white as well and I also used the cerelean blue from the sky to add reflections to the leaves on the outside edges (see below) 
Here I am trying to get realistic clouds. It's harder than it looks folks! I added a very light yellow-cad yellow hue + titanium white- and mixed in a touch of cadmium red hue to add a bit of reflection off the edges of the clouds before I added white to them. 
This last tree I did, I tried using Dalhart Windbergs method and after I put down the first darkest color of pure Pthalo green, I used a #2 rigger and painted individual leaves from the excess paint so they will appear in the background.
I seem to have the habit of making my trunks too large for the size tree I am painting. Note to self!
