Hi, and welcome to Pixelation.
I see you've put quite a lot of time and effort into this, and it's impressive for a first sprite, so let me help you out a bit.
So in your reference the trunks are comparatively narrower against the leaves, so I've made the trunk narrower and the leaves stick out more.
Also, in pixel art, details need to be removed to increase the readability of a piece. For example, the gaps between the leaves. We just leave (hur hur) those out out to make it easier to draw the palm tree, and because then we have more room to give it shading.
See if you can give you trunk and leaves a better shape. Imagine that the tree is really zoomed out and blurry and try to replicate it.