PersistentBinaryTree

   6
 4   7
2 5   10


insert(9)


new_root node (6)

go right as val greater then 6
(create a new node for 6)
also point new_root to 4 (left side)

go right as val greater then 7
(create a new node for 7)
No need to point to left side as already null


go left as val less then 10
(create a new node for 10)
assign new val there.


return new_root