$4)$ Implement a binary search tree to store numbers. Add methods to insert a new number and check for the presence of a number in the tree.

Example:

bst $=$ BinarySearchTree$()$

bst$.$insert$(50)$

bst$.$insert$(30)$

bst$.$insert$(70)$

print$($bst$.$contains$(30))$ # Output: True

print$($bst$.$contains$(40))$ # Output: False