[Answered ]-Expand/Collapsible list of objects

you can figure out what level you’re at in the tree using node.level, so all you need is add an additional CSS class to just the top level, something like this:

<ul id="node-{{ node.pk }}" class="children{% if node.level==0 %} top_level{% endif %}">

node.tree_id could also be interesting instead of just pk