Whirling butterflies. A breeze blew through the trees, and the flowers slowly fell. The word "like" in the sentence reflects that this sentence is a metaphor. The essence is "the flowers on the trees slowly fell." Using a thing similar to the flowers falling slowly. To use an analogy to make the sentence more concrete and vivid, because the slowly falling flowers are very similar to the fluttering butterflies, a breeze blows through the trees and the flowers slowly fall down like swirling butterflies.