Nested menu

Hi all,

is there anyone have same problem when run code from Make it easy to add a nested menu to the Templates · Issue #2314 · holoviz/panel · GitHub.
Error message
ValueError: Loops may only be used inside a DOM node with an assigned ID. The following loop could not be expanded because the

node did not have an assigned id:

{% for k2,v2 in v1.items() %}
                        {% if loop.index0 ==0 %}

how to solve the problem.