illusion can be captured in many ways. in this case, the photo is not a trick photo, but the main subject matter, the red tree, contrasted against the surrounding subject matter, the green trees, presents two starkly different perspectives of the same image, and of the season (spring/summer or fall). in accepting the red tree you have to accept a reality (it is fall) that the surrounding trees oppose (its still spring/summer), hence the illusion is that one or the other should be correct, but not both at the same time in the same picture.
The one strong element I see here is the coloring. Wonderful! I have no way of knowing what is an illusion here though since there are no real clues that I can see. On one hand that can be very good, if the illusion is so good that I can't tell it is an illusion. The composition would be better, I think, if the pretty little red tree were not quite centered. Of course that's just my own opinion. Anyway, this sure does reflect the season. Good luck in the challenge. Grayce aka Gracious
The red tree looks totally out of place, but I see the spot on the ground where it goes in. I see the shadow. I see everything else around it. Pretty good photo also.