Hello, I'm mashkina and I'll do a critique for you today. Hope, it'll be useful.
First, the concept is really beauriful. One can clearly feel the mood of your piece.
Your color choice is very clever, so as a coloring technique you used for the background. the fact that colors don't blend too much helps a lot to see a sky in a sunset on your picture. (yeah, i love the sky a lot)
A tree looks very natural.
The problem I have is with grass. It looks a little glued onto the ground. I'd suggest next time you make thinner strokes but more of them while drawing grass.
About the emptiness of the picture - I see, what you're saying. Maybe add some birds in the sky. Or butterflies. Or some animal under the tree. But on the other hand I like you piece more as it is - simple and beautiful.