To indicate that a task should be a child, it's ParentID should be equal to the ID of the parent task. The parent task should also have it's summary field set to true (or 1 if the field is of type bit). For instance:
Parent (ID: 1, ParentID null, summary 1)
Child(ID: 2, ParentID 1, summary 0)
The dropdown is displayed when you have a selected task, and is used to insert the new task relative to the selected one - as its child, above or below it. When you don't have a selected task, the button simply appends the new task at the end.
I've also attached a sample that uses the events to implement the CRUD operations of a Gantt bound to a List.
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