Crossword Genius

Philatelist to tread on tax official (5,9)

Ross

I believe the answer is:

stamp collector

I'm a little stuck... Click here to teach me more about this clue!

'philatelist' is the definition.
(synonyms)

'to tread on tax official' is the wordplay.
I cannot really understand how this works, but
'to' is within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for stamp collector that I've seen before include "one makes albums" , "Philatelist" .)

I've seen this clue in The Daily Express.
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