DRAWING #1 -(CLOSE UP)- You should be close enough to see the leaves clearly (draw them life size or larger).
Pay attention to detail. Draw only a few. example:

DRAWING #2 - (FULL VIEW) - Draw the entire tree, or almost the entire tree.
Do not make it small, but have it fill most of your page. Step away several yards from the tree.
The shapes of the nearest leaves should still be clear to you, but not large.
Some simplification will be required, but try not to generalize.
Refer to your first drawing to assist you with the naturalistic presentation of the contour lines.
example (unrelated to the above drawing/leaves) :