PPT Slide
In freehand drawing you would use the triangle method discussed earlier. If there were an object on the ground to the left of the tree where the shadow tails, the shadow would shape or mold itself around and over that object. (page 84 in book)
In the above picture we'll assume that the shadow is landing flat on the ground. Also note that shadows tend to get blurry the longer they extend out and their intensity starts to fall off, so once the shadow has been distorted to the correct position you should make it less distinct.Finally, if the tree is growing on a mountainside you would adjust your triangle accordingly as pictured below.