What is the best way to maintain a git public repo fork within a private repo?

Is there a way to fork a public git repo and track them within a private repo? The use case here is to have one private repo while maintaining the ability to pull and merge from the public repo.

Example Directory layout:

myPrivateProject:
  - workDir1
  - workDir2
 开发者_高级运维 - publicRepoDir (cloned from some public repo)

You're looking for a subtree merge.