Unless that is your style, a better palette (cone forest is evergreen) and popping out branches would be a good start. Currently it looks like a cone with several noisy circles on top of it.

some better palette and lighting

It's not pillow shading, but seems to place lights, darks, and highlights without regard for a light source or the form of the object, similarly to pillow shading.

Think about the branches on this tree. You don't have to draw them out, but you should suggest that they're there. Since your light source is from above, that means that the upper parts of the branches should be lit, and they should be casting shadows on branches below.

Don't worry about the colour count just yet, since you're still figuring out how to actually draw what you want to draw. Use as many as you need for now, then simplify your palette later, making pixel-level tweaks as needed.

It may help you to do some drawings at a larger size using reference images (and maybe on paper, if you're not comfortable drawing large on the computer) so help you get a feel for how to draw fir trees (and maybe trees in general). Even if your goal is to make a cartoony tree, taking the time to understand how real ones work will help you a lot. You can't effectively simplify something without understanding it.

I won't contribute as I never tried this kind of tree (but one unsuccessful mockup). But this will help me greatly as well! I think replies in this thread covered how to draw and lit pines so far.

Here is a nice example from a famous game


notice how artist highlights each branch, instead of pillow shading or highliting outlines. And how there are soft shades under the branches (ambient occlusion).

the one from snv i like very much. but yeah the example from the game i don't like.
the tree outer shape looks too symmetric in some versions. the last ones bottom is great. (not just a brown line)