My wife has been using this image as a desktop background for about a year now, but recently I took a good look at it.
Initially I thought this was simply a photo of a tree in silhouette, sliced, colourized and laid out as you see it.
But on closer inspection, it seems that these are shots of the tree, at various times and seasons, with different coloured sky in the background. The website doesn’t really have detail on how the image was created.
The photographer also created Spectrum of the Sky — but I like the Tree better.