Mother at Christmas mad to pinch one bright decoration (8,5)

'decoration' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'mother at christmas mad to pinch one bright' is the wordplay.
I cannot really understand how this works, but
'mad' could be 'cross' (both can mean angry) and 'cross' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'bright' could be 'lit' (similar in meaning) and 'lit' is located in the answer.
'mother' could be 'mary' (Mary is an example) and 'mary' is found within the remaining letters.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?