I do not remember exactly, but I think that's, in the section "foliage", in the third row, I think the third brush starting from the left side, with number 185.
But various brushes from this section are fine to create the tree leafs effect, try yourself with different sizes and opacities, and evaluate the results, maybe you find it other brush that adjust to your needs.
Panel 1: Hmm. That's kinda ... ugly Panel 4: Sorta decent I suppose Panel 5: What the?! The grass?! I ... could try doing that, I hope? Panel 6: Wait wait. So super fine details on a rough base. Okaayyyyy so that's the direction I should go in Panel 7 - last panel: =_= Okay so I have to do all these minute details... which I obviously cannot. I don't think this direction is gonna work for me.