ParentID in item

why does this not work? I mean: defining parentid in item definition.

This is very common situation when getting data from database.

In case of loading data in XML format, component awaits, that parent child relation will be defined by XML structure.
But it possible to achieve similar functionality with different data loading types, when data loaded from CSV of JSArray it possible to encode it in such way … 6299143000
In both cases structure of tree defined by provided parent id