Compressive stress from the top

1. Start by making a cut from the topside. The depth of the cut should be about 1/3rd of the diameter of the trunk, or before the trunk tends to pinch the guide bar.
2. Now cut from the bottom to meet the first cut.

If the trunk is thicker than the guide bar length

1. Start by crosscutting the opposite side of the trunk.
2. Pull the saw towards you and crosscut from the top, up to about 1/3rd of the trunk diameter.
3. Now crosscut from the bottom. If the trunk is lying on the ground, make a bore to avoid sawing stones.
4. Continue with undercutting towards the centre of the trunk. 

NOTE: Observe how the trunk reacts. This method reduces the risk of the guide bar pinching.