Quietly sheltering in very cold tree (6)
I believe the answer is:
poplar
'cold tree' is the definition.
'poplar' can be an answer for 'tree' (poplar is a kind of tree). I am not certain of the 'cold' bit.
'quietly sheltering in' is the wordplay.
'quietly' becomes 'p' (musical symbol).
'sheltering' becomes 'polar' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'p' inserted within 'polar' is 'POPLAR'.
'very' acts as a link.
Can you help me to learn more?
(Other definitions for poplar that I've seen before include "Timber tree" , "Tree - London district" , "Leaves producer" , "part of London" , "Tall tree of north temperate regions" .)