filling treeview from xml file, but only certain tags

[minimalniemand]

I try to recursivley fill a treeview from a xml-file. It works well,
when the contents of the xml and the treeview match 1:1.

code here: http://mad-scientists.co.uk/micha/shownode.txt

a sample xml doc can be found here:

                                mad-scientists.co.uk/micha/CurrentSearch.xml">http://mad-scientists.co.uk/micha/CurrentSearch.xml

the problem is, that the xml file contains more items then I want to
show in the treeview.
I only want to show items with certain tags. (OPTEXT & ITEXT)
The other tags should be used to generate a SQL WHERE clause.
I tried various versions of

if tag = "this" then
   nod=nodes.add(bla, child)
end if

but I simply don't get it to work. I'm desperate!