Sub category items duplicated in main drop down menu

I have created two sub categories (General Fiction and Historical Fiction) for the main category Fiction & Literature. While these two sub categories display correctly in the left hand category menu, i.e. as sub categories of Fiction & Literature, they are duplicated in the main drop down menu.

The subcategories appear in Level 1 of the product drop down menu in exactly the same way as a category does. However, they are also duplicated in Level 2 of the menu as sub categories of Fiction and Literature. It’s this second method of display I want to achieve, i.e. these two subcategories not appearing in L1 of the menu but appearing in L2 only - as, in my opinion, they should do.

Hoping you can help me sort this out, otherwise my L1 menu is just going to get bigger and bigger! Thanks in advance for all help.