title: Is it possible to add a sub collection to a collection without creating document in firestore in android?
body: <p>I am new to cloud firestore in firebase. In my project I created <em>category</em> as collection which is common to all users. But I need to create <em>category</em> as sub collection for each collection. Is it possible?</p>
  
  <p>Any help will be highly appreciated.</p>