Depending on your site structure, you may sometimes want to have a navigation menu with drop-down sub-navigation items but not have the root of the navigation point to anything. For example, you may have a top level menu item called Products but you don’t want a top level Products page; you just want pages for the products. In this case, on mouseover on the desktop, you want a clickable list of the different Products but you don’t want the top level Product menu item to be clickable.
Go to Appearance > Menus
In Edit Menus tab, select Custom Links
Enter # for the URL
Enter your desired text for the top level of your drop-down menu
Click the Add to Menu button
Drag the menu item to its desired position
For the menu item you just added, click the down arrow to the right of the item (it will read custom link” to the left of the item)
Remove the # from the URL. This will convert the link to plain text.
Click on the Save Menu button
There you have it. A simple and clean solution.
Thanks to: https://goo.gl/FozS8y