either this: or this:
As I looked carefully at the tree, trying to figure out a process, I saw that some leaves were touched with light and therefore clearly discernible, while others were in shadow, and therefore bunched together. So I drew the ones that really stood out, floating in air, and then went around them with a vaguely accurate outline of the rest. Then I mixed light, middle, and dark colors of greens. I used the middle and dark almost like a negative painting around the light leaves, leaving them until last to paint.
I wish I had done an even lighter, brighter green for the lightest, and a little darker green for the midtone, just to get more sparkle, but I was pretty happy with this technique.
LEMON TREE -- Micron pen and watercolor.
More practice will undoubtedly improve this process!