title: how to clone an vuedraggable element into its sibling's nested children list?
body: <p><a href="https://codesandbox.io/s/fervent-oskar-shqtp?file=/src/components/nested-draggable.vue" rel="nofollow noreferrer">https://codesandbox.io/s/fervent-oskar-shqtp?file=/src/components/nested-draggable.vue</a></p>
  <p>pull operation is working fine, but when I change the pull prop from 'true' to 'clone', error occurred.</p>
  <blockquote>
  <p>NotFoundError
  Failed to execute 'insertBefore' on 'Node': The node before which the new node is to be inserted is not a child of this node.</p>
  </blockquote>