nest egg vs savings bank

nest egg

noun
  • A saving; a reserve of money. 

  • A natural or artificial egg placed in a bird's nest, to encourage the bird to lay its own eggs there. 

  • An egg squash. 

savings bank

noun
  • A type of financial institution that focuses on retail banking: savings of private depositors, payments, credits and insurances for individuals or small and medium-sized enterprises. 

How often have the words nest egg and savings bank occurred in a corpus of books? (source: Google Ngram Viewer )