The picture is kind of small, but the one on the right really doesn't look like an apple seedling, especially the last few inches of the shoot. Alex

Kolos, first of all, if your intent is to grow beautiful Macintosh apples, this is not a good way to do it. Seedlings are alot like our children. They never look identical to the parent and sometimes look nothing like them. It's difficult to say how the fruit would turn out. There's a good chance the fruit would be small and inferior and maybe not resemble a typical Macintosh. Buy a grafted tree if you want guaranteed results. If you are determined to grow a tree from seed, your method should work. Just a couple pointers...make sure the peat is slightly moist. You might want to add a fungicide. Put it in the fridge (just above freezing) in the fall and check in early spring. When you see little white sprouts, you can put them in one of those tiny greenhouses for seedlings from Lowes or Home Depot. Leave it in a windowsill until temps moderate. Acclimate them slowly to sun and wind (a couple hours a day-gradually increasing). Then plant outside after last frost. Good luck. I've done this succesfully with maple seeds and I don't think apple seeds are too far off. If you are determined to grow a tree

The top looks like the citrus leaf, as it appears to have a petiole. That said, the easiest way, is to pinch off part of the leaf and smell it. The lemon will be obvious. Good luck with your new babies.

Hopefully, I'm not to late to help save this baby and it still have some green buds/shoots and this long post is not for nothing! This was posted in March and your pic is its green as if sprouting or starting to grow, when usually most trees that grow outside are dormant still, especially in Z6a. I do not think that the fact it was grown inside is why this is happening. The mess up in time/temp indoors is bad, but unlikely to actually kill it so suddenly, it will be more of a gradual decline and then death, usually 1 season indoors is not good but will live with minimal growth the following season unless conditions are corrected. My thoughts: Is it possible you brought it outside (march and outside in the pic), and you had a frost or large temp swing indoors/out which possibly killed/injured it which is why the top started to die? Even though apples are cold hardy, if it was never acclimated to the cold to go dormant in the fall and just brought out now, even a light frost can do some serious damage if there is green young leaves. Also, I suspect it is also environmental since damage/death is going top/down at this specific time. Which means roots are possibly somewhat alive at this moment. What I would do if you really want to try and save it: If it's still alive and those sprouting buds are still alive I would make a clean cut right above the last living bud. And if the weather is at or below freezing (during the night as well), and you have an unheated garage or shed take it in their or if not possible try covering it with something. Cool is okay, but not freezing, And let it see the light whenever it gets above freezing. Or you could technically bring it back inside put near bright window until it warms up a bit since it's season/growth clock is already off. If your lucky, you will be left with a tiny stick since it was cut right above the last living shoots, but those living buds/shoots might grow a bit and maybe even sucker over the next couple months...but the goal is to preserve whatever is still alive. If it does survive the next couple months it's a great sign.