This is a low contrast image with subdued tones.
This is totally okay and any further processing should be done with what you had in mind artistically.
You might experiment with global contrast or local contrast changes like USM with large radius.
You might use some manual dodging and burning to increase certain edges - if you want that.
I personally would try to carefully sharpen the tree stems in the background slightly as well as the main tree, while keeping overall contrast low as a starter and maybe cleaning up some of the dark spots in the snow.
The square crop also seems to be a good idea in my opinion, since its already square, right?
Cheers
~Chris
EDIT: P.S.: had a little time at hand and thus attached a suggestion. Cheers ~C.