[Theme: Ari] collapse sub-menu in sidebar

Hi,
I started my website with ari theme.
You can see an example here
On the left there is the sidebar which contains the pages list.
When I create a sub-page (child?) it appears a little bit more on the right, so you can understand which pages are the parents.
There is a way to collapse all the sub-pages, in order to show only the parents pages?
The sub-pages should be visible if the mouse go on the parent…
For example Piano Black Theme do not show as default the child pages…
Please let me know if I need to paste same .php files
Thank you in advance