Format large groups fold/unfold dropdown

I was looking for, (and couldn’t find) a way to format the presentation of groups. Large groups that is.

I would love to be able to implement a dropdown arrow ‘v’ next to the group title, resulting in unfolding the contents of the group, arrow changing into '>" or '^" of course.

Is there any documentation on that. Would be especially convenient on mobile devices/phones.

Also, i would love to have the option of a divider, or break,

Hope you can help.