ChildCollapsed Event
This event occurs when a node is collapsed by user interaction. It is the same as the Collapsed event, but sent to the parent of the TreeviewField.
This event has the following syntax:
on childcollapsed [compositefieldname]
compositefieldname is optional if you specify the event in a script for a composite field, or if the composite field is the frame's top form.
The TriggerNode attribute identifies the node that was collapsed.
More information: