Yes, your XML file should conform to a specific XML DTD.
Here's a demo page with XML datasource example:
http://www.9rays.net/asp.net/treeview/Demos.aspx?demo=program_xml
DTD:
Key CDATA #REQUIRED
Text CDATA #IMPLIED
ToolTip CDATA #IMPLIED
NavigateUrl CDATA #IMPLIED
NavigateTarget CDATA #IMPLIED
ChildNodeType CDATA #IMPLIED
NodeType CDATA #IMPLIED
NodeSrc CDATA #IMPLIED
Expanded (True|False) #IMPLIED
ExpandLevel CDATA #IMPLIED
DefaultStyle CDATA #IMPLIED
HoverStyle CDATA #IMPLIED
SelectedStyle CDATA #IMPLIED
SelectedHoverStyle CDATA #IMPLIED
ImageUrl CDATA #IMPLIED
SelectedImageUrl CDATA #IMPLIED
ExpandedImageUrl CDATA #IMPLIED
SelectedExpandedImageUrl CDATA #IMPLIED
IconSetPath CDATA #IMPLIED
PostBackOnExpand (True|False) #IMPLIED
PostBackOnCollapse (True|False) #IMPLIED
PostBackOnSelect (True|False) #IMPLIED
PostBackOnDeselect (True|False) #IMPLIED
PostBackOnCheck (True|False) #IMPLIED
PostBackOnUncheck (True|False) #IMPLIED
SelectExpands (True|False) #IMPLIED
SelectCollapses (True|False) #IMPLIED
CanBeSelected (True|False) #IMPLIED
IsCheckBox (True|False) #IMPLIED
IsChecked (True|False) #IMPLIED> ]>