Well it looks very much like a form of Eucalyptus. Didn't it have any cultivation instructions?

Nope, it came with nothing but a pretty bow. No info at all. If it's some sort of Eucalyptus should the sap be smelly? The berries stay for months and very slowly turn yellow then orange then red.

It's very easy to look after -it's on the inside doorstep getting watered around once every couple of weeks and I haven't managed to kill it yet.

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It looks very much like a Mistletoe Fig (Ficus deltoidea), though it seems unusually fast growing and vigorous for that.