A rooted Christmas tree is normally grown in a small pot - so the roots are normally shallow and weak, so may not develop deep enough to survive a shift to the garden. The trees also need to have been watered regularly - did you water it weekly even during winter? The brownness can be a sign of many things, lack of water is one of them.

If you post a pic we might be able to advise better about why it is going brown.

it is the growing season for xmas trees,i grow them in pots rather than the ground, so it should be sprouting.it could be a temperature change which has affected your tree,although they say rooted when you buy them some have had the main tap root cut before you bought it if field grown,if this was the case then it won't be as hardy as you might think to start with,until it gets going outside, remember a 2ft/3ft tree is already about 4years old,give it abit of time to accustom itself to the out doors,if you have kept it on the porch then it would have had a wind barrier,give it a while longer,you can prune out any dead bits once it has recovered,i wouldn't feed it just yet either just water water water as i say wait awhile.

Keep it well watered - I suspect Plantmaiden's in the right area, it's the temperature shock - suddenly being exposed to winds, cold nights, etc, having been kept in porch. Would have been best to harden it off before planting, but too late now. Water, as I said, and give it a feed with a handful of fish blood and bone, or Vitax Q4 or Growmore around the base, raked in.

Please don't plant a xmas tree in your garden. Have you seen how large they grow? Try Abies koreana instead for a better garden plant.