The BuildHierarchy() function builds a tree structure over a list of nodes of identical type that are hierarchically related.
The relevant nodes (1st parameter) must have a key field (2nd parameter) that is referenced by another field within the child node (3rd parameter). The function returns a tree with the following structure:

<TreeResult>
	<RootNodes Key='X'>
		<Items></Items>
		<Nodes></Nodes>
	</RootNodes>
<TreeResul>

BuildHierarchy('Node', 'Key'.'Key of the parent node')

BuildHierarchy('//SG_33', '@DE_1082'.'LIN/DG_C829/@DE_1082')

Note: Alternate solution Hierarchiebildung mit der Funktion SplitToArray()