Um, you know, I think this is pretty neat`n`sweet as is. I think the shape and general foliage is good, but perhaps a tiny bit of shading on the bark, darkening sections where you can see under/through the canopy, and perhaps introduce another subtle color into the shades of green you have, (like the slight yellow I used)
And just for a bit more character a small branch lower down with a bunch of leaves.
You can try experiment around with a few things, like the colors, and shading to make it more like you had in mind.
I am also new to pixel art and it is also a coincidence I also had by very first bash at making trees, not just for pixel art but for any style. The trees I made are pretty low res, but not as low res as your one, but perhaps you can get some ideas about interesting shapes and method.
(the row of trees at the top, after a bit of practice)
The method is very simple and quick, I just use cross-hatching of a "line" brush at various levels of darkness, , then copy what i have and paste , re-color/size, then place .. repeat.. a bit of shading .. well here is a timelapse video (
https://www.youtube.com/watch?v=NSrys0PGY28&feature=youtu.be ) ... Perhaps you could gain some ideas about how to build up interesting foliage this way, or not
But I do like yours anyway, It is I feel a nice balance between a realistic looking tree and a cartoon style of tree.
Keep up the good work.
