To add a submenu:
Make sure the menu to which you want to add a submenu is showing in the iDVD window.
Click the Add button (shown below), and choose Add Submenu from the pop-up menu.
A placeholder button labeled My Submenu appears on the menu. It has the default button style for the theme, so you may need to change it to match other buttons on the menu.
Click the placeholder label for the new button once to highlight it, and type a new name for the button.
When you click the label to highlight it, a light blue background appears behind the text.
Using the pop-up menus in the in-place control that appears (shown below), change the typeface, font style, and font size of the button name if you want.