How do I adapt this menu code to add drop down items?

[judgedredd]

Second post in Jason's new (for me) forum.

Jason kindly did a site makeover for me last year using semantic markup. With that the menu code was this:

Code: [Select]

<?php

$config = [
'siteTitle' => 'Matrix Files',
'mainMenu' => [
'Down the Rabbit Hole' => [
'class' => 'rabbit',
'uri' => 'downtherabbithole.php'
],
'Home' => 'index.php',
'About' => 'about.php',
'Computers' => 'computers.php',
'Finance' => 'finance.php',
'Forum' => [
            'class' => 'forumlink',
            'uri' => 'http://matrixfiles.com/hgnb/viewforum.php?f=5', 
        ],        
'Health' => 'health.php',
'Law' => 'law.php',
'MatrixFiles-radio' => 'http://matrixfilesradio.com/',
'Mirrors' => 'mirrors.php',
'Research' => 'research.php',
'Tech' => 'tech.php',
'Contact' => '#contact',
'Donations' => [
'class' => 'donations',
'uri' => 'donations.php'
]
]
];

How do I go about adapting it to include drop down menu items? For example under 'Computers' how can I add - Apple, Amiga, PCs, Sinclair, Commodore - as the items in the drop down? I will also post this question in the 'other' forum.