code: def add_to_list(my_list, my_element):
      
      if isinstance(my_element, list):
          for element in my_element:
              my_list = add_to_list(my_list, element)
      else:
          if my_element not in my_list:
              my_list.append(my_element)
  
      return my_list
docs: Helper function to add new my_element to my_list based on its type.
  
      Add as new element if it's not a list, otherwise extend to the list
      if it's a list.
      It's also guarantee that all elements are unique
  
      :param my_list: A list
      :type my_list: list
  
      :param my_element: A new element
      :type my_element: str, list
  
      :returns: A list with unique element
      :rtype: list