Leaves?
You're starting on so many new trees, but they all look the same. I think we could help more if you posted your reference image, and stopped posting a brand new tree every day. Just stick to one, and work at it for a lot longer than what you have been with these. One nice thing about pixel art is that you can correct your mistakes more easily than in any other medium that I know of, and you don't need to start something completely new just to try to correct some small errors.
Right now your leaves are still just balls of color. Your palm leaves are definitely improving, and that's great, but you really need to just search out what a tree really looks like. Does it only have 4 branches? does it really have four huge inflatable balls impaled onto those branches? You don't need to draw each leaf, but you do need to learn how to imply those leaves with smaller, more controlled blobs of color that emulate the actual compound shape of the leaves.
Here's a quick demonstration:
Those are the blobs of leaves I see in that tree. It's just a matter of picking out where the light hits the leaves and where it doesn't. Obviously you'd normally go into much more detail with a serious piece, where you'd find the blobs of many more different shades to where you could see some of the leaves, you'd pick out where the background peeks through the leaves, you'd pick out the parts of the exposed branches, you'd pick out the texture of the trunk; you'd go as far as you and your schedule could stand. Your ability and tolerance will get higher and you'll be able to get further into details more easily over time.
On a side note, notice the ratio of leaf-to-trunk. The trunk looks tiny compared to the leaves because they hide most of the trunk and branches from view.
While I don't suggest tracing the image of any tree for a serious piece of artwork, you can be justified in trying to get a sense of what shape the blobs really are with some tracing around. After you get a feel for how these shapes really look, you can try eyeballing it for your real piece. It will always be off, and don't worry about that, just try to get it as close as you can. Don't try to manipulate it or guess for something, try to find it in the image and imitate whats there, even if it feels like it would be wrong.
Just really try to see what actually makes the tree look like a tree.
