Please solve this question. This is related to recursion and induction. You may use 'base case', 'step case'. Thank you so much!

CExercise 121. Assume that N is a set of numbers, namely Z, Q or R. (a) Draw the following tree: tree3(tree 2, tree_5(tree 2, tree 1)) (b) Define a function sum: FBTrees N * N which sums up all the labels that occur in the tree (compare Example 6.2 where the analogous operation for lists is defined). (c) Apply your function to the tree from part (a). (d) Give the code for a function that performs the same job for an object of class BTree. (e) Justifying each step show that if the set of labels is N \ {0} then for all binary trees t we have not