Best way of displaying complex directory structure to user

The use case is users come to a website and create an advert. Usually they just create one advert. So the way to manage this would just to have a list of their adverts they have run in a table.

The issue comes when they want to run many adverts as part of a campaign so its a layer above the individual advert. This is fine for folks that want to run campaigns and they could just have a table that lists campaigns.

The problem we have is we've built the system around campaigns so the user who just wants to run one advert at a time has to navigate around this architecture. ie create campaign first then create an advert within the campaign. It's not intuitive and users don't understand the concept when they join.

So my question really is: I want one interface where a user can see a list of campaigns and adverts in the same table. I guess like you would see a folder structure where a diretory can include single files (an advert) or a folder (a campaign).

I don/t think there's anything inherently wrong with this approach? Is this the best approach?