Please see the below example:

Code:
Imports System.ComponentModel

Public Class level1Collection(Of T As level1Item)
    Inherits BindingList(Of T)

    Public Sub Load()
        Dim i As T = Me.AddNew
    End Sub
End Class

Public Class level2Collection(Of T As level2Item)
    Inherits level1Collection(Of level2Item)
End Class

Public Class level3Collection(Of
...