How to use different user controls into stencil in the WPF Diagram (SfDiagram)?

<Grid>
     <TextBlock Text="Shapes" FontSize="17" FontWeight="SemiBold" 
                       Foreground="#2b579a" HorizontalAlignment="Left" Margin="10,5,0,5" Grid.Row="0"/>
     <stencil:Stencil x:Name="stencil" Grid.Column="0" Grid.Row="1" ExpandMode="All" BorderBrush="#dfdfdf" BorderThickness="0,0,1,0">
         <stencil:Stencil.SymbolGroups>
             <stencil:SymbolGroups>
                 <stencil:SymbolGroupProvider MappingName="Key"/>
             </stencil:SymbolGroups>
         </stencil:Stencil.SymbolGroups>
         <stencil:Stencil.SelectedFilter>
             <syncfusion:SymbolFilterProvider SymbolFilter="SymbolFilter">
             </syncfusion:SymbolFilterProvider>
         </stencil:Stencil.SelectedFilter>
         <stencil:Stencil.SymbolSource>
             <local:SymbolCollection>
                <syncfusion:NodeViewModel  UnitHeight="50"   Key="Controls" UnitWidth="70" ContentTemplate="{StaticResource custombuttontemplate}">
                    <syncfusion:NodeViewModel.Content>
                        <Button Content="Button"/>
                    </syncfusion:NodeViewModel.Content>
                </syncfusion:NodeViewModel>
             </local:SymbolCollection>
         </stencil:Stencil.SymbolSource>
     </stencil:Stencil>
</Grid>