An issue tree breaks the client's question into smaller questions you can answer one at a time. Good trees are MECE: mutually exclusive (no idea fits two branches) and collectively exhaustive (every possible cause has a home).
Ways to split that are MECE by design:
- By math: profit = revenue - costs; revenue = customers × spend.
- By process: the steps a product or customer goes through, in order.
- By segment: customer groups, regions or products that don't overlap.
- By opposites: internal vs external, new vs existing.
Two tests: pick any idea and ask whether it could sit in two branches (an overlap). Then ask whether there’s a cause no branch would catch (a gap). Interviewers care more about a clean first layer than a deep tree.