Use the TreeView.NoExpandImageUrl property to specify a custom image for the non-expandable node indicator. The non-expandable node indicator image (or spacer) is displayed next to leaf nodes (in place of the expandable and collapsible node indicators) to align the leaf nodes with parent or root nodes.

When the TreeView.ShowExpandCollapse property is set to true, the System.Web.UI.WebControls.TreeView control displays a plus sign (+) or minus sign (-) or a placeholder image next to a node to indicate whether the node is expandable, collapsible, or non-expandable, respectively. You can specify custom images by first setting the TreeView.ImageSet property to TreeViewImageSet.Custom, and then setting the TreeView.NoExpandImageUrl, TreeView.ExpandImageUrl, and TreeView.CollapseImageUrl properties to the URLs of the custom images. If no images are specified, the default images are used. To hide the expansion node indicators, set the TreeView.ShowExpandCollapse property to false.

The value of this property is stored in view state.