What is the best way to level a tree log?
It is also possible to do the final smoothing of the rough squared off faces by using a router. The router rides in a set of movable supports that you arrange over the end of the log and the router bit can cut to a smooth finish across the whole log face. As you make each pass with the router you slide the movable supports over an appropriate amount and then take the next pass. 

The starting point is to afix (clamp) a frame of two straight boards in parallel along each side of the log. Then at right angles to these you have the router support slides. The router makes passes by feeding the router along the support sliders. The next pass is arranged by moving the sliders along the first parallel support boards. The following picture attempts to show a top down view of the setup.