[berendka]

Nested Sets

https://en.wikipedia.org/wiki/Nested_set_model

You can ust to store tree structures in relational databases for faster querying stuff like "all nodes below node x", "How many nodes to the top node" and so on.

Querying is easy, but comes at the cost that changes like inserting and deleting are more expensive.

I used this for an auth service with roles, user and org units. pretty query heavy, worked very well.