Hi Vince,
sorry but I don't understand what is this udf field. UDF stands for? User Define Function/Field ?
Listen, I think on this: the field could be a lookuplist or a string field in this case. Or it is something different?
If you manage it as a lookup list you have always to create dynamic list rappresent the tree items and assign the list to the field at runtime. It could be not so performant for the system I think.
Let me know if you'd like to do something like this.
Ciao,
Massimo.