Crack inside tree from the east producing shrub (6)

I believe the answer is:

myrtle

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'shrub' is the definition.
(myrtle is a kind of shrub)

I cannot understand how the rest of the clue works.

(Other definitions for myrtle that I've seen before include "Shrub with purple-black oval berries" , "Evergreen shrub with dark purple berries" , "Fragrant evergreen shrub" , "Plant with aromatic blue-black berries" , "Evergreen shrub - try elm (anag)" .)

I've seen this clue in The Independent.

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