Sub menu diaplay issue on a mobile phone

I have a site where I have a top menu which has 4 or 5 main items, with sub-options under them. On a PC monitor the menu shows correctly, you hover over the main item and it expands so you can see the sub-options.
When displayed on a mobile phone I have the menu selector off-canvis, but when you click it you see all of the menu items in a single list. Is it possible to have it display only the 4 or 5 main menu items on a mobile and you click them to expand to see the sub-options - in the same way it displays on a PC monitor?

Live Url please.
And please use for the first menu item a "seperator"

Thanks - site is here - www.wick-academy.co.uk/

Hello,
here is an instruction how you can do it like an accordion menu
yootheme.com/support/question/88179?order=modified