<ItemsControl.GroupStyle>
                <GroupStyle>
                    <GroupStyle.HeaderTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Name}" />
                        </DataTemplate>
                    </GroupStyle.HeaderTemplate>
                    <GroupStyle.Panel>
                        <ItemsPanelTemplate>
                            <StackPanel Orientation="Horizontal" />
                        </ItemsPanelTemplate>
                    </GroupStyle.Panel>
                </GroupStyle>
            </ItemsControl.GroupStyle>

CollectionViewSource.GetDefaultView(this.DataContext).GroupDescriptions.Add(new PropertyGroupDescription("Group"));
        CollectionViewSource.GetDefaultView(this.DataContext).GroupDescriptions.Add(new PropertyGroupDescription("CreateDate"));