In reality a group of leaves arises from one of the arms of the tree. The groups lie in front and behind each other because a tree is not a flat thing. I’ll show you two ways how to draw them.
Exercise 1:
Draw each step before moving on to the next step.
Step 1: above the trunk you draw as lightly as possible circles right through each other. The circles don’t have to be perfect! Each circle represents one group of leaves.
Step 3: choose in the other circles (groups of leaves) which are in front and which are behind. Each time erase the lines of the underlying circle.
Step 5: now draw leaves within each group. Let them point in different directions.
Exercise 2: DRAWING IN GRAYSCALE
Using a soft pencil, sketchily fill in the entire shape of a tree in dark gray, without clear outlines. Use a good eraser (or kneaded eraser) to create light spots for the leaf clusters, as in exercise 1. Darken the shadows in other areas, such as between the leaf clusters, deeper within the tree, and on any shadowed sides (in my example, the light comes from the right). Finally, add some details that will help you identify the leaf shapes—not too regularly, not too precisely. If you were to draw a landscape with trees outdoors, learning to distinguish between grayscale values would be very helpful.
DIFFERENT TREE SPECIES
In exercise 1 I started with circles as basic shapes but different types of trees may of course have other basic shapes. Later you can make those basic shapes leaf-like again. In this way you can even make a real Christmas tree (the bottom two).
EXTRA 2: draw as lightly as possible one or more of the following tree models. Look at the tree in real life or photos of the chosen tree species. For example, in a weeping willow the leaves point downwards like tears. You can also make the drawn leaf groups gray immediately and then continue with light and shadow as in Exercise 2.
A Christmas tree. Start with the two clusters in the middle just above the trunk, zigzagging from bottom to top.