Fig. 4
Two kinds of structure for the identical node {v,c1,c2,c3}. a A sub-structure embedded in the whole tree that node v has multiple children, node {c1,c2,c3}. b The binary transformation of a structure that node c2 and c3 firstly merged as node u then node u becomes the new child of node v. It turns out the binary structure b always has the smaller structural entropy