WPF TreeViewItem default icon for each parent node - wpf

Question

How would I add an icon to each of these parent nodes
I tried adding under each TreeViewItem but the icon doesn't show and when I bind my collection to the ItemSource, it says it must be empty fist.
<TreeView x:Name="tvMessages" HorizontalAlignment="Left" Height="262" Margin="10,37,0,0" VerticalAlignment="Top" Width="248">
<TreeViewItem x:Name="itemsCritical" Header="Critical">
<TreeViewItem.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Description}"/>
<TextBlock Text="{Binding ID}" Visibility="Hidden"/>
</StackPanel>
</DataTemplate>
</TreeViewItem.ItemTemplate>
</TreeViewItem>
<TreeViewItem x:Name="itemsAlert" Header="Alert">
<TreeViewItem.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Description}"/>
<TextBlock Text="{Binding ID}" Visibility="Hidden"/>
</StackPanel>
</DataTemplate>
</TreeViewItem.ItemTemplate>
</TreeViewItem>
<TreeViewItem x:Name="itemsInformational" Header="Informational">
<TreeViewItem.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Description}"/>
<TextBlock Text="{Binding ID}" Visibility="Hidden"/>
</StackPanel>
</DataTemplate>
</TreeViewItem.ItemTemplate>
</TreeViewItem>
</TreeView>

Answer 1

Take a look at this example:
<TreeViewItem Name="treeViewItem1" IsEnabled="True">
<TreeViewItem.Header>
<StackPanel Orientation="Horizontal">
<Image Height="16" Source="Images/16x16_red_lamp.png" Width="16" />
<TextBlock Margin="5,0" Text="HostA: Disconnected" />
</StackPanel>
</TreeViewItem.Header>
</TreeViewItem>
Just place the Image inside and tell the Source where is your Icon located.
You can also use HeaderTemplate in case you have Bindings against associated item.