changer le background d'un TreeView en wpf

Bonjour,
j'ai defini la propriété Background de mon TreeView mais aucun effet
Code:
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  <TreeView Background="{DynamicResource ResourceKey=SuperDegrade02}"
                          >
 
 
 
                    <TreeViewItem  Margin="10" >
                        <TreeViewItem.Header>
                            <StackPanel Orientation="Horizontal">
                                <Image Source="/Images/arrow_up.png" Stretch="Uniform" Margin="3" Height="16"/>
                                <TextBlock Text="GESTION" VerticalAlignment="Center" Margin="5" HorizontalAlignment="Right"
                                   FontSize="14" FontWeight="Bold"/>
                            </StackPanel>
                        </TreeViewItem.Header>
 
                        <StackPanel Orientation="Horizontal">
                            <Image Source="/Images/database.png" Stretch="Uniform" Margin="3" Height="16"/>
                            <TextBlock Name="txtStockage" Text="Stockage" Margin="3" MouseDown="txtStockage_MouseDown"
                                       VerticalAlignment="Center"  HorizontalAlignment="Right"
                                   />
                        </StackPanel>
 
 
 
 
                        <TreeViewItem  Margin="3">
                            <TreeViewItem.Header>
                                <StackPanel Orientation="Horizontal">
                                    <Image Source="/Images/a_profile.png" Stretch="Uniform" Margin="3" Height="16"/>
                                    <TextBlock Text="Personnel" VerticalAlignment="Center" Margin="5" HorizontalAlignment="Right"
                                   />
                                </StackPanel>
                            </TreeViewItem.Header>
 
                            <TextBlock Name="txtCaisse" Text="Caissière" MouseDown="txtCaisse_MouseDown" Margin="3" />
                            <TextBlock Name="txtGestionnaire" Text="Gestionnaire" Margin="3"  MouseDown="txtGestionnaire_MouseDown"/>
                        </TreeViewItem>
 
                        <StackPanel Orientation="Horizontal">
                            <Image Source="/Images/a_saved_data_utility.png" Stretch="Uniform" Margin="3" Height="16"/>
                            <TextBlock Name="txtEtsData" Text="Vos données" Margin="3" MouseDown="txtEtsData_MouseDown"
                                       VerticalAlignment="Center"  HorizontalAlignment="Right"
                                   />
                        </StackPanel>
 
 
                    </TreeViewItem>
 
 
</TreeView>
Si quelqu'un sait comment le faire ,je suis prenant.
Merci.