thats unique...the wing cuts. over here we use something similar to prevent barber chairing of species like ash and elm{trees that are stringy in structure if peeled.
the object is to place your notch/scarf in
.....plunge{bore}cut behind your notch{whatever amount of hing wood you want, ...thats how far back you start your plunge cut. try to make it as flat and even as possible.} be sure you plunge cut extends to back of tree and is stopped several inches from going out other side.
you can now either continue to cut directly threw or you can pull out saw...assess situation... then when ready cut off those few inches of holding wood that you left.
this allows you to allows felling without barberchaing or saw pinching
