PPT Slide
Here is a complicated shadow of a tree beginning to be drawn in PhotoShop. The desired angle of the tree shadow will of course be determined by the direction from which the light is coming. Let's say the sun would be coming from the right side of the image. You can see this if you look carefully at the tree trunk, as the right side of the tree has an orange glow to it from the sun and the left side of the tree is dark, or in the shadow area.
This would mean that the tree shadow would fall to the left and be placed flat on the ground.In PhotoShop you would move the transform center pivot point to the bottom of the tree, and then adjust and distort the shadow to the desired angle.