categories expand and only display titles in content window

Hi,

I need help to make this.
I’ve made my problem more vissible here:
https://www.arjanversloot.com/example.gif

I hope someone understand what I mean and can help me.

If it’s nessacery I will pay you for it.

I’ve looked allready for plugins, but didn’t find the right one.

Many thanks

Greetings,
Arjan Versloot