Expand Tabs from Left side and resizing the rest

Hi, 

how can I make tabs on the left side that are per default collapsed (see picture) and which should expand to the right side resizing the rest of the window (Grids, etc). I've made the tab on the left side setting TabStrip left but I can't do the rest. there is no collapse property on the tab? 

telerik:RadTabControl   Align="Right" BackgroundVisibility="Collapsed" TabStripPlacement="Left" Grid.RowSpan="4" Grid.Row="1" >
            <telerik:RadTabItem  Header="Something" >
                <telerik:RadTreeView Grid.Row="1" IsDragDropEnabled="True"   Grid.RowSpan="4" >
                    <telerik:RadTreeViewItem Header="Football" />
                    <telerik:RadTreeViewItem Header="Tennis" />
                    <telerik:RadTreeViewItem Header="Cycling" />
                    <telerik:RadTreeViewItem Header="Basketball" />
                </telerik:RadTreeView>
            </telerik:RadTabItem>
        </telerik:RadTabControl>