how do I create submenus in my module? I am pretty new to drupal php etc.

I have a module that just add links to main menu and load a .html and a .js when a link is called. 

For now my menu looks like this:


Demo


Now I would like something  like:


Demo
More demos

extra demo1
extra demo 2



Ideally "More demos" should be collapsed and should expand on click

Here is the code I have so far:

&lt;?php

/**
 * Implements hook_menu()
 */
function kl_menu(){
  $items = array();


  $items['demo'] = array(
   'title'            =&gt; t('Demo'),
   'page callback'    =&gt; 'build_demo_page',
   'access arguments' =&gt; array('access content'),
   'menu_name' =&gt; 'main-menu',
   'type' =&gt; MENU_NORMAL_ITEM,
  );


  return $items;
  }


/*
 * build_demo_page
 */
function build_standard_demo_page() {
drupal_add_js(drupal_get_path('module', 'kl') . '/demo.js', 'file');
 return  ( file_get_contents( drupal_get_path('module', 'kl').'/demo.html') );
}


I am not sure to go from there.

Thanks
I've pasted a sample code below. Hope that helps.     

 function hook_menu() {
      $items = array();

      $items['demo'] = array(
      //other code here
      ); 

      $items['more-demos'] = array(
      //other code here
      );

      $items['more-demos/extra-demo-1'] = array(
      //other code here
      );

      $items['more-demos/extra-demo-2'] = array(
      //other code here
      );

      return $items;
    }