How tall is it? How thick is the trunk?
Do you have a photo of tree with foliage too?
The tree is 21" in diameter & 20 ft. tall. We live on a hill so the photo is not leaning ;) Do we need to remove one of the co-dominant trunks as well? Thank you for the responses.
With the age that this Maple now is, and with the main issue of having two dominant leaders, there is no way to easily fix this tree. Red Maples are notorious for not maintaining a central dominant leader and will constantly develop co-dominant leaders. Without constant attention and pruning, the tree will continue to grow improperly and will at some point in the future, split apart. It is similar to the problem with Bradford Pears, the question is not whether they will split, just a matter of when.
If you remove one of the trunks, you will have a very ugly tree, because you will be removing much of the foliage on one side. Had this issue been addressed when the tree was younger, it may have been corrected. If you remove one side now, the exposed cut will be a large area susceptible to insect, disease, and rot. And even if you remove it, you will have to continue almost annual pruning of the maple to keep it from happening again and again.
My suggestion would be to remove the entire tree and plant a new tree, not one of the inexpensive and popular red maples.
If anyone wants proof of just how bad red maples develop multiple leaders, just drive around almost any commercial parking lot, which are normally full of red maples, and look at how bad the internal structure of the trees develop. Over time, as the tree matures and the weight load increases, something will fail, split, and fall over.
In summary, a red maple can be a beautiful tree, but due to the soft wood, and the tendency for multiple leaders and poor branch angles, the tree will require constant pruning and attention to maintain it in a healthy and strong form. Without giving it this attention, I would recommend a different tree.
I agree with ST...planting a new tree would be best.
You MIGHT get some reassurance by installing a cable between the two trunks but this is NOT a homeowner project. A certified arborist has training and load tables that allow them to calculate where best to put the anchor point. Just a small error in placing them and the limb might crack and fail.
An arborist might also be able to identify a point somewhere up one of the trunks that could be a less damaging pruning point, to save most foliage but not continue bad growth habits.
Thank you for your generous advice.
Aruba, I will try to think of good alternatives to suggest for replanting>