Display editable values in TreeView

I am using WPF to create a TreeView display that shows an XML file. I want all of the treeview to be in editable text boxes. I have managed to make it so my parent node is editable, but the child is not. For example, I have an Xml with Variables, a parent node, and values. The XML looks like this,

'<variables>
      <ParentNode>
          <DataSource>a</DataSource>
          <Catalog>b</Catalog>
          <User>c</User>
          <Password>d</Password>
  </variables>'

I have managed to make my WPF output the following that expands and collapses, however a, b and c are not editable.

 '+Variables`

changes to

`-Variables 
     -ParentNode 
       a
       b
       c`

I am able to do this through XAML with the following code.

 '<Window x:Class="TreeView2.MainWindow"
    xmlns="http://ift.tt/o66D3f"
    xmlns:x="http://ift.tt/mPTqtT"
    Title="MainWindow" Height="350" Width="525">
   <Window.Resources>
    <XmlDataProvider  x:Key="MyList" Source="C:\CAD.Services\MASTER.xml" XPath="variables" />


    <HierarchicalDataTemplate DataType="variables" ItemsSource="{Binding XPath=*}">
            <TextBox FontSize="25" Foreground="Black" Text="variables"></TextBox>
    </HierarchicalDataTemplate>

    <HierarchicalDataTemplate DataType="ParentNode" ItemsSource="{Binding XPath=*}">
        <TextBox FontSize="16" Text="ParentNode"></TextBox>
    </HierarchicalDataTemplate>

    <Grid>
         <DockPanel>
             <TreeView DockPanel.Dock="Left" Width="250" Name="treeViewPackages"
             ItemsSource="{Binding Source={StaticResource MyList}}">
             </TreeView>
        <Grid DockPanel.Dock="Right">
        </Grid>
    </DockPanel>`

I am trying to make it so A B C would be editable like the rest of the options. However I am unsure of how to go about making this happen. They are displayed fine, but are not located inside a text box.

Any help would be greatly appreciated.