I developing some component for Joomla 2.5. I follow official tutorial:
http://docs.joomla.org/Developing_a_Model-View-Controller_Component/2.5/Adding_categories  
Now, I added categories functionality for my component, but when I open categories menu in administrative panel I don't see add, delete, edit buttons...
This is code of helper:
abstract class youtubeHelper
{
        public static function addSubmenu($submenu) 
        {
                JSubMenuHelper::addEntry(JText::_('COM_YOUTUBE_SUBMENU_ITEMS'),
                                         'index.php?option=com_youtube', $submenu == 'items');
                JSubMenuHelper::addEntry(JText::_('COM_YOUTUBE_SUBMENU_CATEGORIES'),
                                         'index.php?option=com_categories&view=categories&extension=com_youtube',
                                         $submenu == 'categories');
                // set some global property
                $document = JFactory::getDocument();
                $document->addStyleDeclaration('.icon-48-youtube ' .
                                               '{background-image: url(../media/com_youtube/images/tux-48x48.png);}');
                if ($submenu == 'categories') 
                {
                        $document->setTitle(JText::_('COM_YOUTUBE_ADMINISTRATION_CATEGORIES'));
                }
        }
}
What I need do for add the buttons?