Early congrats to you, my friend! You may also want to consider getting the moment on video. I did that with my proposal, and every now and then, we cuddle up on the couch and watch it a few times (it's pretty short). More than two years later, it still brings a tear to her eyes.
And if you're open to other suggestions, I have a few (I'm a romantic, at heart):
If she likes games, try doing a scavenger hunt all over the house, with the first clue wrapped like a present under the tree. Have the final clue lead her back to the tree with you kneeling there on one knee. You can have the clues be all innocent and whatnot so she'll be surprised at the end, or they can be romantically linked to your history together to build up the suspense.
If you're not firm on the Christmas tree idea, and you're willing to make your proposal a little more public...
Get some carolers together at a specific spot (you can use your friends, but it'll be more of a surprise if she doesn't know them). Go out for an evening stroll. Have them sing normal Christmas carols, but as you two get closer, they swap some of the words out with ones that are marriage themed. Like for Deck the Halls, instead of "Tis the season to be jolly, fa la la la la la, la la la la..." make them sing "Tis the season to get married, fa la la la la la, la la la la..." When she makes a comment about it, get down on one knee and read your poem. (Obviously, you kneeling is the queue for the carolers to stop singing so she can hear you.)
And if you're open to other suggestions, I have a few (I'm a romantic, at heart):
If she likes games, try doing a scavenger hunt all over the house, with the first clue wrapped like a present under the tree. Have the final clue lead her back to the tree with you kneeling there on one knee. You can have the clues be all innocent and whatnot so she'll be surprised at the end, or they can be romantically linked to your history together to build up the suspense.
If you're not firm on the Christmas tree idea, and you're willing to make your proposal a little more public...
Get some carolers together at a specific spot (you can use your friends, but it'll be more of a surprise if she doesn't know them). Go out for an evening stroll. Have them sing normal Christmas carols, but as you two get closer, they swap some of the words out with ones that are marriage themed. Like for Deck the Halls, instead of "Tis the season to be jolly, fa la la la la la, la la la la..." make them sing "Tis the season to get married, fa la la la la la, la la la la..." When she makes a comment about it, get down on one knee and read your poem. (Obviously, you kneeling is the queue for the carolers to stop singing so she can hear you.)