Grouped WPF ListView Styling issue with margin

Question

There is a tiny margin on the left side in the style when using the grouping functionality of the ListView in WPF.

Sample of ListView with grouping problem (margin):

Sample of ListView without grouping (want same style of item in grouped list):

Question:

How to remove the margin/padding? The (selected) item in the grouped list should fill the same space as in the ungrouped list.

Update:

            <ListView Margin="20,0,0,0" ItemsSource="{Binding ItemsView}" SelectedItem="{Binding SelectedItem}" IsSynchronizedWithCurrentItem="True"  SelectionMode="Single" BorderThickness="0" Background="Transparent">
                <ListView.GroupStyle>
                    <GroupStyle>
                        <GroupStyle.HeaderTemplate>
                            <DataTemplate DataType="data:Item">
                                <DockPanel HorizontalAlignment="Stretch">
                                    <TextBlock Text="{Binding Name}" FontWeight="Bold" Margin="0,5,5,5" />
                                    <Separator  />
                                </DockPanel>
                            </DataTemplate>
                        </GroupStyle.HeaderTemplate>
                    </GroupStyle>
                </ListView.GroupStyle>
                <ListView.ItemTemplate>
                    <DataTemplate DataType="data:Item">
                        <TextBlock Margin="10,10,10,10" Text="{Binding Name}" />
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>

Answer 1

When grouping is used in a CollectionViewSource (I'm assuming you are using one), the, Groups will be visualized by a GroupItem. The default style of a GroupItem looks like this (obtained with StyleSnooper):

<Style TargetType="{x:Type GroupItem}" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
    <Setter Property="Control.Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type GroupItem}">
                <StackPanel>
                    <ContentPresenter Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" />
                    <ItemsPresenter Margin="5,0,0,0" />
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

As you can see, there is a Margin on the ItemsPresenter. A solution is to create your own style for the GroupItem, and remove the Margin on the ItemsPresenter, and set the GroupStyle.ContainerStyle to use this style.