The trunks in these first three trees still look a bit like lampposts or sticks. I show you how to make a tree trunk a bit more realistic.
Exercise: Draw the outline of a trunk a little shakily (left). A knot here and there also looks real. You can decorate your tree trunks in all kinds of ways with lines or shadow. When you are outside, notice the different types of trunks. Even a smooth tree trunk is not as clean as a lamppost.