How to add an element with attributes into an existing Xelement?

Hello I want to dynamically add the branch element which you can see in the xml code down 1 to N times to the code. It depents on the numbers of branches the company is in.

<branch key=<%= propertycheck(xml, "branch") %>/>

But I did not find out yet how to add an element which looks like this

<branch>

I only found ways to add elements like this :

<branch></branch> 

My Plan was to add the branch elements first and after that the Attributes. But If i can create both in one operation, its also good^^

Cheers Steven

<address

                                firstname=<%= attributecheck(xml, "firstname") %>
                                lastname2=<%= attributecheck(xml, "lastname2") %>
                                lastname=<%= attributecheck(xml, "lastname") %>>
                                <function key=<%= propertycheck(xml, "function") %>/>
                                <position key=<%= propertycheck(xml, "position") %>/>
                                <saluation key=<%= propertycheck(xml, "saluation") %>/>
                                <nameaddition key=<%= propertycheck(xml, "nameaddition") %>/>
                                <acadtitle key=<%= propertycheck(xml, "acadititle") %>/>
                                <departmentcode key=<%= propertycheck(xml, "departmentcode") %>/>
                                <language key=<%= propertycheck(xml, "langauge") %>/>
                                <branch key=<%= propertycheck(xml, "branch") %>/>
                                <country key=<%= propertycheck(xml, "country") %>/>
                                <addresssource key=<%= propertycheck(xml, "addresssource") %>/>
                                <addresslock key=""/>

                            </address>