Kind of shot up tree (3)
I believe the answer is:
gum
'tree' is the definition.
(I know that gum is a type of tree)
'kind of shot up' is the wordplay.
'kind of shot' becomes 'mug' (I've seen this in another clue).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'mug' in reverse letter order is 'GUM'.
(Other definitions for gum that I've seen before include "Sticky stuff - tree" , "Leaving body" , "Sticky substance and mouth tissue" , "Eg, a eucalyptus" , "Glue; jelly-like sweet" .)