How to Uncheck checkboxes in TreeView programatically WPF

In the treeView, i load the Xml file using a HierarchicalDataTemplate. When the checkbox is checked i get the checkbox values and update it to a list.

But i want to have a button function to uncheck all the check-boxes in the treeView programmatically, How can i do this? Please help me.

<XmlDataProvider x:Key="questions" XPath="Questions/Question" /><HierarchicalDataTemplate x:Key="rootTemplate"><HierarchicalDataTemplate.ItemsSource><Binding XPath="child::*" /></HierarchicalDataTemplate.ItemsSource><StackPanel Orientation="Horizontal"><!--<CheckBox Name="checkBoxTree" CheckBox.Checked="TreeView_Checked" IsChecked="{Binding IsChecked}"/> --><CheckBox Name="checkBoxTree" Checked="TreeView_Checked" Unchecked="checkBoxTree_Unchecked" /><TextBlock Text="{Binding XPath=@Name, Mode=TwoWay}" /><TextBlock><Hyperlink NavigateUri="{Binding XPath=@WebSite}" RequestNavigate="Hyperlink_RequestNavigate"><TextBlock Text="{Binding XPath=@WebSite}" /> </Hyperlink>    </TextBlock></StackPanel></HierarchicalDataTemplate>

TreeView:

<TreeView Name="TreeViewer" HorizontalAlignment="Left" Height="183" Margin="38,126,0,0" Grid.Row="1" VerticalAlignment="Top" Width="750" Visibility="Collapsed"  FontSize="15" 
   ItemsSource="{Binding Source={StaticResource questions}}" ItemTemplate="{StaticResource rootTemplate}"  ></TreeView>

Function to un-check the check-boxes programmatically:

 private void buttonReset_Click(object sender, RoutedEventArgs e)
        {

           //Need to know how to how un-check the check-boxes programmatically?

       }

Thank you for your help.

Karthik