wpf Treeview itemtemplate 默认选中第一节点
<TreeView Grid.Column="0" Grid.Row="0" Grid.RowSpan="3" ItemsSource="{Binding ProductsList,IsAsync=True}" >
<TreeView.ItemContainerStyle>
<Style TargetType="TreeViewItem">
<Setter Property="IsExpanded" Value="True"/>
</Style>
</TreeView.ItemContainerStyle>
<HierarchicalDataTemplate ItemsSource="{Binding ProductsModel}" x:Key="TreeViewTemplate">
<WrapPanel>
<TextBlock x:Name="a" Text="{Binding Name}">
</TextBlock>
</WrapPanel>
</HierarchicalDataTemplate>
</TreeView>
如何默认选中第一个节点,我这里没有TreeViewItem.isSelected.我这是MVVM的模板,求大神