To add product categories as menu items may be confusing sometime.As products and products categories were from woo commerce Plugin,they do not directly appears on the menu selection area in WordPress dashboard.
Steps to add product categories in menu
First of all go to your dashboard > Appearance > menu
Then at the top of your dashboard,you will have screen option button.Click there and you will have a drop down to select product categories for menu item.Select product categories and look below in menu selection area.You will have product categories to select as menu item.
