Add node or element to XML

I do have an XML like,
<student><class><name>Ram</name><age>23</age></class>
<class><name>Sam</name><age>26</age></class>
<class><name>Ban/name><age>28</age></class>
</student>
My requirement is, I would like to add another node inside <class>,
by checking Condition - for age less than 23 = Bsc, less than 28 MCA, greater than 28 Bsc
<student><class><name>Ram</name><age>23</age><Degree>Bsc</Degree></class>
<class><name>Sam</name><age>26</age><Degree>MCA</Degree></class>
<class><name>Ban/name><age>28</age><Degree>Bcom</Degree></class>
</student>
< ...