This is the original digital photograph.  What makes this a poor photo is also what makes it a good candidate for editing.  There are two main values here, (value= the degree of light to dark) the tree and ground are pretty much the same dark value and both set against a light value in the sky.
The overall design though I like, the tree fills the area nicely and the slight diagonal of the ground plane makes it interesting.

Here I have lightened the whole picture and increased the contrast to help the Magic Wand tool do it's work.
(Colors / Adjust / Brightness - Contrast)
You have to do some playing here with the settings, to much and you'll burn out the fine detail of the smaller branches.

Select the Magic Wand tool, the tool options settings I used were Match Mode: Brightness / Tolerance: 50 / Feather: 0
Click on an area of the sky, then go to Selections / Modify / Select Similar, this should have all of the sky surrounded by the selection marquee except for the finest branches.