Sketch a tree and branches on the left, with a tall main trunk. Show the bark on the side of the trunk with long up-and-down lines. Use short horizontal lines for the tree on the right, a birch, which has a smaller main trunk.
When filling in lines on the birch, notice that the lines are roughly horizontal, not vertical like the other tree's. These trees look pretty bare, so we'll give them leaves in the next step.