I was thinking about this- and depending on the size of the tree (which I don't know), I'd be inclined to wrap it in fleece.
This is the standard advice and it works well for normal winters and moderately hardy plants. However it just slows down the heat loss to the point where short snaps get deflected, but experience tells me it can't cope with a week without a thaw. Eventually the temperature will drop below zero. Fleece does allow the winter sun to warm the plant quickly (even when it can't create anywhere near a thaw).
This latter point persuades me to think this advice migrated here from well inside Europe or the Americas where cold weather is often bright and sunny during the day. This creates conditions inside the fleece
that resemble Northern California where short moderate frosts are surrounded by balmy days, so many fruit species from further south manage to survive with superficial damage.
The conditions in New England do involve cloudy frosts much worse than ours, and their traditional answer is to use blackened oil drums of water inside the frame or shelter - this is very effective here. I have used it to grow Strawberry Guavas successfully for decades. The water in the metal container provides masses of latent heat as it freezes, and doesn't stop giving until the whole drum is frozen. This can stop plants freezing, but they have to be able to cope just above 0C - no good for toms or most peppers, but very good for Meyers. I haven't tried C.pubescens yet - I'm still building my stock.
One thing stopped all of these methods saving my plants in Dec 2010 - they all eventually run out of steam in a relentless freeze. Mainly because of that low sun - the wan pom sun as the Aussies call it. We think of Alaska, Kamchatka and Newfoundland as very far north but they are on or south of 51.5 where London is.
The only thing that is inexhaustible here (where we don't have permafrost) is ground heat stored since Summer. That's why I want to tap into it.