Why is the aspen crooked? For me it takes all the focus. This aspen also looks like it is crammed against the left and top edges of the canvas (is that why it is bent?) - "sorry, you have to end here dear tree, there is no more space.".
Just my 2c what may be "wrong" with the aspens.
Other than that, the composition looks good, and you have used a full value range. As suggested by arnieb, you probably want to soften the edges of the distant mountains.
One thing worth considering is to do a bit of cross pollination of color - now you have what looks like three distinct "bands", the upper blue/white, the middle purple, and the bottom yellow/green. How about introducing some purples in the foreground shadows (subtle - to harmonize), and perhaps consider the color of the light (afternoon? yellow/golden?) and the effect this has on the sky...
Regarding the foreground pine, you can't really add to it - it already has a full value range (from darkest dark to highlights) - if you want it to pop in some way, you need to tone down the background. If you want the greens to look more green, consider adding some subtle reds (not in the pine though