Wolmart has a built-in mega menu that can be enabled on every First Level menu item in the Appearance > Menus tab.

Make the most of your menu following step by step:

Step 1: Add a First Level menu to build as megamenu.

Step 2: Check Megamenu option and set Megamenu Width, Megamenu Position.

Step 3: Add direct child menu item to it. It should work as menamenu columns.

Step 4: Add direct child menu item to menamenu columns menu item. It should work as menamenu subtitles.

Step 5: Add menu items to menamenu subtitle menu item.

Step 6: Finally,  click the Save Menu button to save your megamenu.