To enable 'LoadOndemand' feature for a node, the node property, 'ExpandMode' should be set as 'ServerSideCallback'
<obout:Tree ID="ObClassicTree" ClientObjectID="obTreeClientObj" DataSourceID="XmlDataSource1" EnableViewState="false" LoadingMessage="Refreshing..." CssClass="vista" runat="server" Width="200px"> <DataBindings> <obout:NodeBinding DataMember="employee" ExpandMode="ServerSideCallback" TextField="name" ImageUrl="~/obout.ajax.ui/treeview/examples/img/engineer-icon.png" /> </DataBindings> </obout:Tree>