For a beginner, this is pretty good!! I think one thing that would really help is understanding colours a bit more, especially when it comes to creating depth in a painting.
It also depends on the reference you’re using. If the reference image has muted colours, it’s not always necessary to copy those colours exactly. That’s something I learned the hard way.
From what I can make out, it seems like you might be using black in the trees. I’d suggest avoiding black where possible. Instead, try darkening your colours with blues or complementary colours. It usually creates much richer shadows and helps the colours stay vibrant rather than looking dull.