myDiagram, the diagram being inspected:

myVisualTree, showing the Layers, Nodes and Links that are in myDiagram above:

You can also try selecting, copying, and deleting parts in myDiagram and then click on "Draw Visual Tree" again to see how the visual tree in myDiagram changes.

See also the Visual Tree sample, to show the same visual tree using nodes and links in a traditional tree structure.