It's a conifer seedling of some sort. Angiosperms - flowering plants - usually (but not always) germinate with a pair of cotelydons (first leaves) whereas conifers (Gymnosperms or cone bearing plants) produce a whorl of foliage like in the photo.

What kind of conifers are close by? That could nail things down a bit but it is really difficult to be more specific until the little guy has grown on more.

A pine tree is one example of a CONifer. The clue is in the name.

As floral uk said, conifers are cone producers. Pine, fir, hemlock, cedar, etc... the lacy shape your seedling was exhibiting in the photo is a result of the seed casing stuck on the end holding the needles together. That has probably fallen off by now. Transplant yours into a pot and slowly you can watch your tiny seedling grow into a beautiful and stately pine (if that is indeed what it is). -

Very often pine seeds arrive in mulch, and more often than not are southern yellow pine ...... which might or might not be hardy where you live. I use southern yellow pine bark extensively (such that I buy by the pallet) for making soils and mulching the gardens/beds, so the image you uploaded is a very common sight around here. BTW - it's very unlikely to survive for any length of time indoors.

Al

Please update us when your seedling updates you! Love it.