I would like to reproduce the great idea behing the CMS UI and Static Page UI. there is a left sidebar, once clicked, a second sidebar bar appears with a list of items. once clicke, the main panel is updated with a new tab and the corresponding data and form. This is a great UX for a user in my case, i dont want the user to go back and forth between the backend list of 15000 company and one company form. hence im looking into building this second left sidebar with the backend list inside.

Does anyone any idea or insight on how this is done ?