offshoot vs tree fork

offshoot

noun
  • That which shoots off or separates from a main stem or branch of a plant. 

  • That which develops from something else. 

tree fork

noun
  • A bifurcation in the trunk of a tree giving rise to two roughly equal diameter branches. 

How often have the words offshoot and tree fork occurred in a corpus of books? (source: Google Ngram Viewer )