In Tree and Sky, what three kinds of skies do trees meet?

Trees among trees and the sky meet three kinds of skies: spring, summer and autumn. According to relevant public information, the tree takes root in the earth and points directly at the sky, expanding the artistic conception of space. Trees experience spring, summer and autumn, waiting for the winter when snowflakes bloom in the air, so they have the artistic conception of time, thus revealing the eternity of natural laws.