Users of the following discussion seems to use ICustomTypeDescriptor in order to display a list of expandable custom items in the PropertyGrid.
http://wpftoolkit.codeplex.com/discussions/357764
Maybe some kind of build-in Generic list that implement ICustomTypeDescriptor that could do the job directly would be appropriate
http://wpftoolkit.codeplex.com/discussions/357764
Maybe some kind of build-in Generic list that implement ICustomTypeDescriptor that could do the job directly would be appropriate