One step at a time is the key to this situation.
The top end of the fallen tree is being supported by its limb ends on the ground. You need to remove portions of each limb end to lower the tree. You'll need to judge how the weight of the tree is compressing the wood at its ends, as those limbs will pinch the bar of your saw if you don't get it right. By paying close attention to the kerf in each cut you can generally get the bar clear before it gets pinched. If you cut up from below the limb, you'll avoid getting pinched. Also, be ready for some of that spring-tensioned wood to jump when it's released. Taking small chunks--firewood length--will likely avoid any mishap.
With each cut, the tree will lower itself. Toward the end of this process you may find the broken stem is still attached to the base of the tree. At that point, just fell the remaining spar to one side or the other. Take your time and think about what's happening at each stage and you should be fine.
One other factor, which is hard to know from the photo, is if the fallen tree is tight against its neighbor, that can complicate matters as well. It's all a matter of understanding what gravity and other forces are doing as you alter the situation with each cut.