how to access all items and subitems of treeview in wpf c#

Question

how to access all items and subitems of treeview in wpf c#

i have a treeview like this

<TreeView Name="TreeView1">

<TreeViewItem Name="Pak" Header="Pakistan">

<TreeViewItem Header="Karachi"/>

</TreeViewItem>

<TreeViewItem Header="India">

<TreeViewItem Header="Mumbai"/>

</TreeViewItem>

</treeview>

i want to access all items and sub items of treeview1 and put them into list how to do this?