WPF: TreeView in WPF/XAML

How to use the TreeView Element and loading it through code.

The XAML is as below. We can have any number of nodes in a tree. there is no limit for that Each new TreeViewItem that is added is made into blue color for easy understanding.

<Page 
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 

xmlns:sys="clr-namespace:System;assembly=mscorlib" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" >

<TreeView>

 <TreeViewItem>

<TreeViewItem.Header>

  <TextBlock Text ="Hello"></TextBlock>

</TreeViewItem.Header>

     <TreeViewItem Header="First element"/> 

     <TreeViewItem Header="Second element"/>

     <TreeViewItem Header="Third element"/> 

     <TreeViewItem Header="Fourth element">

<TreeViewItem>

            <TreeViewItem.Header>

<TextBlock Text ="Inside Fourth"></TextBlock>

            </TreeViewItem.Header>

            <TreeViewItem Header="Is there an end to this?"/>

</TreeViewItem>

  </TreeViewItem>

  <TreeViewItem Header="World"> 

<TreeViewItem Header="Again a first element"/> 

  </TreeViewItem>

</TreeView>

</Page>

The Output will be as follows:
Both the nodes are not expanded

First Node(Hello ) is expanded

The Node inside the node is expanded. (Fourth element)

The Node inside the node inside Node is expanded. (Inside Fourth Node)

The Tree is expanded entirely