First let me say, it's very uh... Kawaii. I know I told myself never to use that word but it's the only word that can describe this thing.
Right now I'm pretty sure it's a stylistic thing, but that tiny character of yours seems to be staring blankly into the distance, which is odd given the sidescroller perspective of this game. At least the character, as well as the current tree (trunk) seems to suggest that. Lack of pupils suggests the character is being hypnotized (so I added some in the edit), but that's just me. If the target audience of this game is people who are more familiar with these sorts of expressions, and tend to think otherwise, go ahead and take that direction.
If you're getting stuck on the grass tiles, although I don't know if you are or not, try looking at some examples of well-done isometric grass tiles, quite a few tossed around the forums. They're basically the same thing. Shouldn't be much of a difference, if any, when used as reference.
This should be a good example ( but I suppose you're aiming for an even more stylized approach, like moderately sized leaves patterned along the ground. Might wanna toss in a few "star" leaves in there for good measure.
Here's an edit. The purple color on the canopy was bothering me. Put a shadow beneath it, which I'm pretty sure is what "grounding" means. To further amplify this, roots now pop up from the ground. A bit of highlighting on dark leaves. Redid the trunk; highlights on trunk looked strange and distracting and there wasn't much of a shadow that the canopy casts on it. And bonus character design, which I hope retains the "cute" look you were going for while giving you some inspiration. I couldn't really figure out his/her gender, but I'm pretty sure it's female now.
And if I may, it originally seemed pretty off-balance, (especially the taller one,) so I built off of the more midgety one and just stretched that out.
(Also, are you a weeabo--