Why is the Tree widget empty?

Hello,

I am confused as to how to properly use the Tree widget in one of my mashups.

So let's say that I have an infotable containing two properties: name & sensorType.

Certain rows in the infotable can share the same sensorType value which I want to be the parent of the Tree widget.

I have set the following widget settings as follows:

LabelField: name

TooltipField:

ValueField:

IDField: name

ParentIDField: sensorType

Why is the widget empty?

Thanks in advance.