wpf treeview增加图片的问题（急需）

Question

 <TreeView.Resources>
                <Style TargetType="{x:Type TreeViewItem}">
                    <Setter Property="HeaderTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <StackPanel Orientation="Horizontal">
                                    <Image Name="img"
                                   Width="20"
                                   Height="20"
                                   Stretch="Fill"
                                   Source="6bf20561315aa3b19167da828c7e4649.ico"/>
                                   
                                    <TextBlock Text="{Binding}" Margin="5,0" />
                                </StackPanel>
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </TreeView.Resources>
这个只能对所有节点用一张图片，我希望可以根节点是一张，下面子节点又是另外一张，请问如何实现?