Mystery of my "evergreen" plum sapling.

in Fruit & veg
My 5 plum saplings that were grown from seed/stone in 2019 have been outdoors all winter thus far. 4 of them lost their leaves soon after putting them outdoors in the autumn.
They were altogether outdoors in 2lt pots.
Mysteriously to me, but possibly not to the knowledgeable members on here, one of the saplings has retained it's leaves-see photo. Why is this?
Maybe there is a variety of plum that is not diciduous?
I have not googled this as yet, and prefer to call on the experience of the forum.

They were altogether outdoors in 2lt pots.
Mysteriously to me, but possibly not to the knowledgeable members on here, one of the saplings has retained it's leaves-see photo. Why is this?
Maybe there is a variety of plum that is not diciduous?
I have not googled this as yet, and prefer to call on the experience of the forum.

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If you live in Derbyshire, as I do.
Some weeds seem to mimic other non weed species.
I planted some horse chestnuts here & there along the canal a while ago. When I have later tried to find them, I have struggled. But while looking I found a weed that looked very similar to the HC leaves, there were lots of this specific weed. I had to do a "double take" That is probably coincidence?