To display data in a tree, a data source should contain two additional fields. The first field must contain unique values. Its name is specified by the KeyFieldName property. The second field must contain values that indicate parent nodes for the current node. Its name is specified by the ParentFieldName property. Columns bound to these fields are called service columns.
Note
The data types of the data source fields specified by the KeyFieldName and ParentFieldName properties, must be the same. These values (key and parent) cannot be equal for a node.
To learn more, see Binding to Self-Referential Data Structure.