I selected and grouped the trees and the panel truck. I added a drop shadow to the group using these settings. I didn’t check the Collapse to one layer box because I want to distort the shadows. I ungrouped them and selected a tree.  In the Objects:Floater List palette I select the shadow floater of the tree.

I opened the Distort dialog box (Effects/Orientation/Distort…).  By dragging the handle at the top of the bounding box down and to the left I obtain the effect I am looking for. Then I turned the Opacity slider down to 85% to lighten the shadow. I regroup the shadow and tree, and then click on the Trim button to help reduce the file size. Next I added a single light to the right side of the tree. I did the same to the other two trees and the truck.  Below is what they now look like.