Welcome to your interview.
The question is on your right: Choosing Storage for Tree Data. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
What database technology would you select for a system that needs to store and query hierarchical, tree-structured data? Defend your choice between SQL and NoSQL.