Your question is Simplified Keynote-Style App Data Model. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design a simplified Keynote app for iOS (the key decision is the Slide struct / data model, including nested slides). Asked in the virtual onsite round 1 stage. The author reply says they used slide id plus a level for nesting.