ostensible vs tip of the iceberg

ostensible

adj
  • Apparent, evident; meant for open display. 

  • Appearing as such; being such in appearance; professed, supposed (rather than demonstrably true or real). 

tip of the iceberg

noun
  • A small indication of a larger possibility; the first part encountered of a problem that is much bigger than it seems. 

How often have the words ostensible and tip of the iceberg occurred in a corpus of books? (source: Google Ngram Viewer )