How insert Works

1. To insert N into an empty tree T, return (make-leaf N).

2. To insert N into a nonempty tree T,
   • If N < (root T), create and return the tree whose:
     • root is (root T)

     • left subtree is the result of inserting N into (left-subtree T)

     • right subtree is (right-subtree T)

   • Otherwise (N > (root T)), create and return the tree whose:
     • root is (root T)

     • left subtree is (left-subtree T)

     • right subtree is the result of inserting N into (right-subtree T)

Writing insert is Exercise 8.6.