code: public function setRootType(Contao\DataContainer $dc)
  	{
  		if (Contao\Input::get('act') != 'create')
  		{
  			return;
  		}
  
  		// Insert into
  		if (Contao\Input::get('pid') == 0)
  		{
  			$GLOBALS['TL_DCA']['tl_page']['fields']['type']['default'] = 'root';
  		}
  		elseif (Contao\Input::get('mode') == 1)
  		{
  			$objPage = $this->Database->prepare("SELECT * FROM " . $dc->table . " WHERE id=?")
  									  ->limit(1)
  									  ->execute(Contao\Input::get('pid'));
  
  			if ($objPage->pid == 0)
  			{
  				$GLOBALS['TL_DCA']['tl_page']['fields']['type']['default'] = 'root';
  			}
  		}
  	}
docs: Make new top-level pages root pages
  
  @param Contao\DataContainer $dc