My friend Will and I made some benches for students to sit on when attending my courses. Will had seen these made and used as trestles by carpenters in Romania.
Two four inch diameter logs are split in half to form the legs. One end of each leg is reduced to a wedge shape as you can see below.
We marked the shape of the leg tops onto a Wych Elm log with charcoal and then made a series of cuts
then I chiseled out wood with a knife and batton to form the grooves for the legs to go into.
Each leg was then knocked into its groove and if necessary minor adjustments were made to produce a tight fit.
Once all four legs are in, you can cut off the bottoms of the legs to achieve the ideal height.