Description of fair racecourse? (7)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

I had no idea what was going on here although AINTREE was obvious from ‘racecourse’. Google advises: “Aintree Fair” usually refers to the popular Aintree Antique and Collectors Fair, a large monthly event held at the iconic Aintree Racecourse near Liverpool. Who knew?  I had this down as two definitions and  thought it one of the most feeble of that type I have ever seen in a Times crossword because  they are linked to the same venue. On reflection I think it’s just a cryptic definition, but I still don’t care for it . Edit: Oh well, you can’t win ’em all! Thanks to vinyl1 for pointing out the correct wordplay: ‘fair’ = A IN TREE (fir).