Mark Tree node expandable
<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" HorizontalAlignment="Center" VerticalAlignment="Center"> <TreeView> <TreeViewItem Header="A" IsExpanded="True"> <TreeViewItem Header="B" /> <TreeViewItem Header="C" IsExpanded="True"> <TreeViewItem Header="D" /> <TreeViewItem Header="E" /> </TreeViewItem> <TreeViewItem Header="F" /> </TreeViewItem> <TreeViewItem IsExpanded="True"> <TreeViewItem.Header> <StackPanel Orientation="Horizontal"> <Ellipse Fill="Blue" Width="15" Height="15" /> <TextBlock Text="Third top-level item" /> <Ellipse Fill="Blue" Width="15" Height="15" /> </StackPanel> </TreeViewItem.Header> <TreeViewItem Header="Child a" /> <TreeViewItem Header="Child b" /> <TreeViewItem Header="Child c" /> </TreeViewItem> </TreeView> </Page>