Currently, there is no way to configure the Graph item programmatically or declaratively to show lines or different background colors for the parent and child nodes.
We can see how in some more complicated scenarios it can become difficult to identify parent and child relationships. In such cases it might be more appropriate to show the different level of nodes on separate graphs, or different parent nodes on separate graphs (e.g. one graph for Devices and another for the other group at the same level).
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