Include parent and child items of GtkTreeStore in GtkEntryCompletion

I have a GtkEntryCompletion declared as follows:

<object class="GtkEntryCompletion" id="search_entry_completion">
    <property name="model">menu_treestore</property>
    <property name="text_column">0</property>
</object>

The model is a GtkTreeStore with two columns, and column 0 is rendered as the text that should appear in the entry completion. The problem is that as it is a GtkTreeStore, only the parent items are used in the completion.

So, for example, if I have:

test0
    test00
    test01
test1

Only test0 and test1 will be available for the entry completion. I can't change the model to a GtkListStore, so, is there a way to make all items of the GtkTreeStore available for the entry completion? I'm using Python and Glade for the development of that task.