Look at which limbs are carrying the weight of the tree. They may be resting on the ground hard, broken off and sticking into the ground or shattered and resting on the ground. Ask yourself: What part of the tree is heaviest, and which way is it leaning? What limbs pull it in that direction. Once you think you know what is happening; it can be useful to stand uphill, grab limb, pull; and see how the tree moves. Is it super solid where it is, or is it thinking of rolling one way or the other? Start slow, and if needed attach a rope so you are in a safe zone when you move things. Once you think you know which way things might move, cut back non-weight bearing limbs trying to keep the weight balanced. Check frequently to see how the removal of those limbs is affecting the balance of the tree. Keep asking: Which direction does the weight of this tree want to move in, how will my next cut affect the balance and how do I cut things and stay safe? Usually cutting the branches off the top side will be relatively safe and it will reduce the number of things that might hit you if the tree does move. Eventually you will get to a place where you can get the trunk on the ground, and then it's easy. But it really is all about figuring out what where the weight is and what way it wants to go.