Parts of the tree one catches on (5)

I believe the answer is:

twigs

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'one catches on' is the definition.
(I've seen this before)

'parts of the tree' is the wordplay.
'parts of' indicates taking the first letters (I've seen 'part' mean this).
'tree' becomes 'wigs' (I can't explain this - if you can you should believe this answer much more).
The initial letter of 'the' is 't'.
't'+'wigs'='TWIGS'

Can you help me to learn more?

(Other definitions for twigs that I've seen before include "Small branches" , "Kindling" , "Slender woody shoots" , "Catches on" , "Understands" .)

I've seen this clue in the Evening Standard.

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