Define a Binary_tree class derived from Shape. Give the number of levels as a parameter (levels==0 means no nodes, levels==1 means one node, levels==2 means one top node with two sub-nodes, levels==3 means one top node with two sub-nodes each with two sub-nodes, etc.). Let a node be represented by a small circle. Connect the nodes by lines (as is conventional). P.S. In computer science, trees grow downward from a top node (amusingly, but logically, often called the root).