Adding website logo as the first top level menu item in tb megamenu
You are looking for Menu Icons module.


  This module allows you to upload an image in the menu-item's
  configuration form. After uploading the image, the icon data will be
  added to the menu link's options array.
  
  When a menu link is goes through the theme layer, it will receive an
  extra class which by default is used to attach the images as a
  background image to the corresponding menu item. These class names are
  also compatible with Nice Menu's.