Start with the minimum structure needed to show direction, usually two to four main branches, and only add sub-branches that affect the first analysis step.

Depth is useful only when it changes what you would test. A long opening can hide prioritization rather than demonstrate it.

State the major branches, flag the one you want to start with, and keep additional sub-questions in reserve for when the case reaches that branch.

Practice giving your structure in about a minute, then ask yourself whether every spoken sub-point would change your next action. For a related reference, see What NOT To Do in the First 5 Minutes of a Case Interview.

I ran into this in a mock too. The hard part for me was noticing it early instead of trying to fix everything at once.