You might try posting you question the Trees Forum here. Link below........

Here is a link that might be useful: GW Trees Forum

i have seen trees with wyes cabled - but typically its done by a professional tree service - because it can be dangerous if not done properly.

Remove the weaker half of the tree and prune top heavy branches off the stronger remaining half. Don't top the remaining half.

I had a huge old mulberry tree with a total trunk diameter of about 7 feet that fit the description you provide. Meaning that the trunk looked split but still growing together for several feet and down to the ground. It had been cabled together a couple of times previously but I didn't realize it when I bought this place. The cables were attached to huge eye-bolts that were screwed into the main trunks. My inurance company insisted that I remove the weaker looking part of the tree that hung over the driveway but I still ended up losing the tree eventually. A couple of years ago a combination of heavy winter rains that softened the soil and then an ice storm on top of that. The actual demise of the tree was an electric pole that was a few feet away. The heavy ice caused the pole to come down and it took the tree with it because the wires caught the tree and caused the whole thing to come down on both of my vehicles and left us without power, phone, heat and water for three days in the middle of winter when the temperatures rarely went above freezing. Had I know the eventual outcome, I would have given up the tree earlier and planted a replacement. Good luck with yours!
spiderwoman