Q5. Please solve this question.

5. Let Bin Tree be the inductive set defined in the lectures. A subtree of t e Bin Tree is t itself or a subcomponent of t that is a member of Bin Tree. a. Define a function subtrees : Bin Tree + set(Bin Tree) that maps each t e Bin Tree to the set of subtrees of t. b. Prove by structural induction that, if t e Bin Tree contains n Branch nodes, then t has at most 2n +1 subtrees