There are some Farmville users that lost their Farmville Christmas Tree with different reasons, but the usuall reason aside from accidentally selling the Christams tree inside the gift box or accidentally deleting the tree is the Farmville bug that Farmville team is working on.

Here the message coming from Zynga:

Thank you for contacting Zynga Customer Support. The “FarmVille has been enhanced” message that you are experiencing is a pesky little bug affecting many of our users that we are working hard to fix. If we weren’t big into organic produce we’d probably just douse your farm in pesticides, but for safety’s sake we’ve decided to track this bug down on our own. Thanks for bearing with us while we sort this out, we hope to have this resolved for you shortly. However as a workaround please follow the link and check whether you get the lost item. Answer Title : Loading/Connection Troubleshooting 101 Answer Link : http://zynga.custhelp.com/app/answers/detail/a_id/600

So if your Christmas tree was lost, just drop by on Zynga website and inform them that your Chritmas tree was lost, but of course you have to tell the reason why your Christmas tree was lost. And hopefully, your Christmas tree will be back to your farm.