Some up in eucalyptus tree (4)
I believe the answer is:
pine
'tree' is the definition.
(pine tree is a kind of tree)
'some up in eucalyptus' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'PINE' can be found hidden inside 'up in eucalyptus'.
(Other definitions for pine that I've seen before include "A tree to grieve for" , "Long - timber" , "Fir tree; languish" , "Yen - tree" , "Mope; tree" .)