Heal half of the German tree (5)
I believe the answer is:
alder
'tree' is the definition.
(I know that alder is a type of tree)
'heal half of the german' is the wordplay.
'half of' suggests halving the letters.
'the german' becomes 'der' ('the' in German).
'heal' cut in half is 'al'.
'al'+'der'='ALDER'
(Other definitions for alder that I've seen before include "Tree with toothed leaves and cone-like fruits" , "Tree whose bark is used in tanning" , "New Forest resident" , "Artificial fishing fly" , "Tree or shrub of the birch family" .)