Does this get us into the whole range of "oak and ash and X"? There are many songs with oak and ash and some other tree in the chorus, some mentioned in the ballad index entry above. Some are:
   the six listed at the top of the thread
   North Country Maid
   Home Boys Home
There is a keyword @tree on these and other tree songs in the DT, but the current online search is not picking this up well.
Oak and Ash and Thorn [A Tree Song] is not related to this group.