docs: def tree(names):
      """Show the tree of the collection(s) specified."""
      # query
      query = Collection.query
      if names:
          query = query.filter(Collection.name.in_(names))
      else:
          query = query.filter(Collection.level == 1)
      # print tree
      tr = LeftAligned(traverse=AttributeTraversal())
      for coll in query.all():
          click.secho(tr(coll))