Notes a bunch of spies in shrub (6)
I believe the answer is:
acacia
'shrub' is the definition.
(I've seen this before)
'notes a bunch of spies in' is the wordplay.
'notes' becomes 'ac' ().
'bunch of spies' becomes 'CIA' (Central Intelligence Agency).
'in' means one lot of letters goes inside another.
'a'+'cia'='acia'
'ac' placed within 'acia' is 'ACACIA'.
(Other definitions for acacia that I've seen before include "Thorny tree, wattle" , "Flowering tree or shrub" , "(Sub)tropical shrub with yellow or white flowers - wattle" , "ornamental tree" , "Locust tree the false one" .)