A binary op-tree is heterogeneous (mixed data types), binary tree where all the leaves are the operands and all the non-leaves are the operators. The children of a node containing an operator are the operands on which it operates.

A regular m-ary tree has exactly 0 or m children per vertex. Thus a "regular" binary tree has exactly 0 or 2 children per vertex or node.

Question: This kind of a tree is always, never, or sometimes "regular"? Why?