ObservableCollection < ObservableCollection < Customer > > ????

Question

I'm finding ObservableCollection(ABC)

with ABC has got string HeadCustomer{set;get;}

and

ObservableCollection(T)T = class Customer {string Id{set;get;};string Name{set;get};int Age{set;get}}

Code sample ObservableCollection < ObservableCollection < Customer > >

If you see that, please tell for me.