A Trixie wraps three selections into four bets — the three possible doubles and the one treble. Unlike a straight treble, two winning legs still return something: the double they form survives the third leg's failure.
Total stake is four units. The structure suits picks around evens; on short favourites the doubles pay too little to justify the extra units, and on longshots the plain treble's bigger payout usually beats the insurance.
£1 Trixie (£4 total) on three picks at 2.10. All win: 3 doubles × £4.41 + treble £9.26 ≈ £22.50. Two win: one double returns £4.41 — nearly the whole £4 outlay back. A plain £4 treble would have paid £37 for all three but zero for two.