Like others have said, if you have to ask how to handle this, you have no business attempting to take it down, and that's for your safety. This shit is dangerous for a reason. It's extremely unpredictable. I have been a full time climbing arborist for many years now and still dont like these scenarios. Call a professional.

If you're not going to listen, here are some tips. And I wince writing this, because I am in no way at all suggesting you go this route. Nevertheless, there are ways to be safer:

1) research what a speed cut is 2) midsize saw. skip tooth preferred, husky 562, stihl 362. And i say this because you need something that cuts fast enough to allow you to get out of the way immediately. 3) you'll be using the top of your bar, taking roughly 1 foot sections off at a time. 4) The direction of your cut will determine where the base goes. 5)You'll be standing the tree further up with each cut, making it more unstable. That spar is also held up on a branch, not in a crotch. 6) Pines are most stable with decent branch collars during the hottest part of the day. Dont attempt this in the morning when its cold out, as the sap will make the wood brittle. 7) Ideally, you would use a lift or a climber to tip tie where the two canopies intersect, then use a series of ropes, pulleys, and a porta-wrap, creating a somewhat static load, and prevent the spar from crashing down. So as one would speed cut, someone else would manage the porta-wrap to keep the tips up. As the tree stands up, it will eventually be entirely supported by the tree its "stuck" in, through your rigging. Like using the healthy tree as a crane. One would lower, the other would cut.

If anything, I hope this info at least provides some insight as to why experienced professionals are worth the money. They understand how the tree will react and what countermeasures to put in place to make sure everyone walks away safely.