More clear structure representation

[ClemensLinnhoff]

Is your feature request related to a problem? Please describe.
In the current structure overview of the individual model classes, it is sometimes hard to see which element is a child of which parent.
For example here, you have to really look closely to see if the Upper_Leg is a child of the Hip or on the same hierarchy level:

Describe the solution you'd like
Is it somehow possible to make this a bit clearer? I think increasing the indentation would already suffice.

[FKlopfer]

It is generally not easy to create a hierarchical tree in Asciidoc. We are currently using PlantUML for that (as described here https://nikostotz.de/blog/tree-in-asciidoctor.html). We will look into that if it is somehow possible to increase the indentation.