I LOVE this! And I would love to do this for my bedroom (I have blue walls, too, but a bit darker), but I'm not terribly artistic. Did you freehand the pattern, or did you use tracing paper, or ...?
I drew the tree shapes freehand in pencil on the back side of the paper, then, after cutting, I erased any lines that I could see from the front (the margin, for example). The beauty with cutting tree branch silhouettes is that you can more or less take them wherever you like as long as they continue to taper. I did have my eye on my neighbor's maple tree as I was drawing, so that helped.
There may be some viable options online to trace as well, but I'd support going freeform first, if only to give it a try.
Go for it!
Super cool! There's a real artistry to revealing an image without having any "positive" line cut off from the rest of the paper. Thanks for the link, the compliment, and the further inspiration!