code: protected ListedHashTree cloneTree(ListedHashTree tree) {
          TreeCloner cloner = new TreeCloner(true);
          tree.traverse(cloner);
          ListedHashTree clonedTree = cloner.getClonedTree();
          if (!clonedTree.isEmpty()) {
              Object firstElement = clonedTree.getArray()[0];
              Controller samplerController = ((AbstractDynamicThreadGroup) firstElement).getSamplerController();
              if (samplerController instanceof VirtualUserController) {
                  assert owner != null;
                  ((VirtualUserController) samplerController).setOwner(owner);
              }
          }
          return clonedTree;
      }
docs: had to copy it from ThreadGroup