title: Add firestore collection value without document
body: <p>Hi I am new to firebase firestore And I can't add object directly into the collection see the image <a href="https://nimb.ws/d5DsZO" rel="nofollow noreferrer">wrong result</a>  and <a href="https://nimb.ws/L7YjH9" rel="nofollow noreferrer">expected result</a></p>
  <p>Tried</p>
  <pre><code> admin.firestore()
          .collection('/user/DVCeb96fLKNAeVo1YIbukAOWMI12/balance/')
          .doc()
          .set(userBalance)
  </code></pre>
  <p>It creating a new document under balance collection but I need its Object value directly inside the balance collection</p>