@Override
    public SliceNode getNextSibling(@NotNull SliceNode element) {
      AbstractTreeNode parent = element.getParent();
      if (parent == null) return null;

      return element.getNext((List) parent.getChildren());
    }
 @Override
 public SliceNode getParent(@NotNull SliceNode element) {
   AbstractTreeNode parent = element.getParent();
   return parent instanceof SliceNode ? (SliceNode) parent : null;
 }