Visual Studio .NET - treeview control

Hi!
I have a big problem when to load a treeview dynamically. How can I do? It works fine when I do it in the code-behind file, but I will do it in the html-file with.
I will take the value from the variable str (serverv-value) and put it directly to the treeview controls treenodesrc attribute?? 
Here is some sample code...
<%Dim str as string
   str="<?xml version='1.0' encoding='utf-8' ?><TREENODES><treenode text='F6281-014961' ChildType='Link'><treenode text='F6281-014558' ChildType='Link'><treenode text='F666'></treenode><treenode text='F6281-011527' ChildType='Link'/></treenode><treenode text='F6281-014960' ChildType='Link' navigateurl='test.aspx?varde=Niklas' target='frm_knapp'><treenode text='F6281-014560' ChildType='Link'/></treenode></treenode></TREENODES>" 
%>
<mytree:TreeView id="oTree" runat="server" autopostback="true" treenodesrc=strang>.....
<mytree:TREENODE TEXT="Some list" EXPANDED=true CHILDTYPE="folder" />
</mytree:TreeView>

e.g., oTree.TreeNodeSrc=str;
or you can iteratively build the tree, (here its "Treeview1"):
public void doTree(){
TreeNode x = new TreeNode();
// create our main node...
x = new TreeNode();
x.Text = "<B><font face=Tahoma Size=3>Hotlinks </font></B>";
Treeview1.Nodes.AddAt(0, x );
// create the childnodes...
TreeNode xx;
xx = new TreeNode();
xx.Text = "C# - Native SQL Provider Sample Speed Tests";
xx.NavigateUrl = "http://www.eggheadcafe.com/articles/20010919.asp";
xx.ImageUrl = "http://www.eggheadcafe.com/images/save.gif";
Treeview1.Nodes[0].Nodes.Add(xx );
xx = new TreeNode();
xx.Text = "ASP.NET Vs. Classic ASP Performance Tests";
xx.NavigateUrl = "http://www.eggheadcafe.com/articles/20010920.asp";
xx.ImageUrl = "http://www.eggheadcafe.com/images/save.gif";
Treeview1.Nodes[0].Nodes.Add(xx );
xx = new TreeNode();
xx.Text = "Build a C# MS Search WebService with COM Interop";
xx.NavigateUrl = "http://www.eggheadcafe.com/articles/20010916.asp";
xx.ImageUrl = "http://www.eggheadcafe.com/images/save.gif";
Treeview1.Nodes[0].Nodes.Add(xx );
}

Hi again!
Thanks!
When I wrote what you told me... 
oTree.TreeNodeSrc=str
I got the following answer..."There is invalid data at the root level. Line 1, position 1."
if I run the xml-tree in the browser it seems to be correct so I dont know really...
Whats wrong now??

This is a reply on an old question from me...I wonder?
When I wrote what you told me...   
<%Dim str as string 
   str="<?xml version='1.0' encoding='utf-8' ?><TREENODES><treenode text='F6281-014961' ChildType='Link'><treenode text='F6281-014558' ChildType='Link'><treenode text='F666'></treenode><treenode text='F6281-011527' ChildType='Link'/></treenode><treenode text='F6281-014960' ChildType='Link' navigateurl='test.aspx?varde=Niklas' target='frm_knapp'><treenode text='F6281-014560' ChildType='Link'/></treenode></treenode></TREENODES>" 
%> 
<mytree:TreeView id="oTree" runat="server" autopostback="true" treenodesrc=str>..... 
<mytree:TREENODE TEXT="Some list" EXPANDED=true CHILDTYPE="folder" /> 
</mytree:TreeView>
I got the following answer..."There is invalid data at the root level.  Line 1, position 1." 
if I run the xml-tree in the browser it seems to be correct so I dont know really... 
Whats wrong now??