This one is easy, but so powerful!
Show your bestselling categories in your top-level menu, but put the rest in an "Other categories" dropdown.
If you have other more informational menu items, put them in a “Information” dropdown.
This say, you nudge people toward your bestselling categories and reduce clutter from less important menu items.
I recommend using click data from heatmaps or sales data if you don’t know which categories are your bestsellers.