Clear example of the Object-Relational Mismatch
I'm not seeing an explanation of object-relational mismatch there for two reasons:


What are the objects? You've sketched a database table definition and a visualisation, but I don't see a sketch of the application program's structures.
As far as I can see, all of the additional information in the visualisation can be made available in a purely relational database view. I've done this kind of hierarchy visualisation with CTEs.