参考
SAP Hierarchy Nodes：
https://help.sap.com/saphelp_nw73/helpdata/en/4a/245d72b1160456e10000000a421937/frameset.htm
SAP Annotations for OData Version 2.0：
https://wiki.scn.sap.com/wiki/display/EmTech/SAP+Annotations+for+OData+Version+2.0
TreeTable Odata binding:
https://blogs.sap.com/2015/10/23/treetable-odata-binding/#jive_content_id_2_Hierarchy_using_annotations
