django-sitetree sitetree_items always empty

Question

I've set up the tree using the GUI.
This works well:

{% load sitetree %}
{% sitetree_menu from "mainmenu"  include "trunk" %}

This does NOT:

{% load sitetree %}
{% for item in sitetree_items %}
    ITEM: {{ item.title_resolved }}<br/>
{% endfor %}

The for loop generates nothing.

What am I doing wrong here?

Versions: django-sitetree 1.9.0 python 3.5.2 django 2.0

tree admin screenshot