TreeView HeaderContent Template

This blog describes how to able to place controls in the header content template in threeview. see the below example you will get idea 

 <TreeView HorizontalAlignment="Left" Height="307" VerticalAlignment="Top" Width="397" Name="filterableTreeview">
            <HeaderedContentControl>
                <StackPanel Width="273" Orientation="Horizontal">
                <Label Content="Search"></Label>
                    <TextBox Width="227"></TextBox>
                </StackPanel>
            </HeaderedContentControl>
        </TreeView>