Try changing your treeview code once like below
<asp:TreeView ID="TreeView1" runat="server" DataSourceID="XmlDataSource1">
<DataBindings>
<asp:TreeNodeBinding DataMember="Collection" TextField="Name" />
<asp:TreeNodeBinding DataMember="Box" TextField="Name" />
</DataBindings>
</asp:TreeView>
XML
<?xml version="1.0" encoding="utf-8" ?>
<Collection Name="Server 1">
<Box Name="MB1"></Box>
<Box Name="MB2"></Box>
<Box Name="MB3"></Box>
<Box Name="MB4"></Box>
</Collection>