uPart one is a recursive function tree$-$insert that takes a tree and a number and returns the tree with the number inserted.

u

u$($tree$-$insert $8())$ should return $(8)$

u$($tree$-$insert $12\text{'}(8))$ should return $\text{'}(8((12)))$

u$($tree$-$insert $3\text{'}(8))$ should return $\text{'}(8((3)()))$

u$($tree$-$insert $12\text{'}(8((3)())))$ should return $\text{'}(8((3)(12)))$

u$($tree$-$insert $4\text{'}(8((3)(12))))$ should return $\text{'}(8((3((4)))(12)))$