Eg, alder or birch (4)
I believe the answer is:
tree
I believe this clue is a double definition.
'eg alder' is the first definition.
(alder is a kind of tree)
'birch' is the second definition.
(I've seen this before)
(Other definitions for tree that I've seen before include "Oak, for example" , "Large growth" , "Forest plant" , "Large, woody perennial plant" , "Eg, elm or oak" .)