What is a good user experience for a single web page that allows the user to add and manage 3 related things?

In my case I want the user to see this in the UI:

```
Property 1
   Building 1
      Apartment 1
      Apartment 2
Property 2
   Building 1
   Building 2
      Apartment 1

```

I tried showing it like that with expandable widgets, but it quickly becomes a mess. Not to mention it is a headache to add new buildings or apartments in this mess I created.

Any ideas?