what is this plant?

I had a pot with a dead fern in it (one of the divisions off the Boston Fern last year) sitting idly in windowsill. Had been sporadically watering it for the faint possibility the fern revivied, but instead this came up.

I don't know what it is. Its growth habit reminds me of the avocado, definitely behaves like a baby tree (didn't start with seedling leaves and then true like the veggies I've grown). It has narrow straight-edged leaves wider at the tip, with notches on the wide end.
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Gah. I put this plant out on the balcony for some sun and forgot to bring it in at night. Something ate the leaves. And all the new leaves off my Sage in the adjacent pot. Which was the only living herb I had left.