Miniature tree (6)
I believe the answer is:
bonsai
'miniature tree' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bonsai that I've seen before include "Japanese method of growing miniature plants" , "Japanese plant or tree grown in miniature form" , "The art of growing ornamental dwarfed plants" , "Dwarfed ornamental tree or shrub" , "Mini-tree growing" .)