trees the first two symbols are operandsso we create one-node trees and push pointers to them onto stack nexta is readso two pointers to trees are poppeda new tree is formedand pointer to it is pushed onto the stack nextcdand are readand for each one-node tree is created and pointer to the corresponding tree is pushed onto the stack now is readso two trees are merged for conveniencewe will have the stack grow from left to right in the diagrams