[SOLVED] Custom Menu Child Pages Fold out by Default

Hi,

I created a Custom Menu on my website. Please find it in the bottom menu widget from the left menu bar, called "Indië / Indonesië".
As you can see, the child pages are folded out by default. I would like them to fold out only when the respective parent page is clicked. How can I accomplish this?

Thanks for your help!

Best,
Rutger