Some trees root much easier than others. I can take cuttings from Elderberries, jam them into the ground, and by spring they will have roots and take off. I've tried all kinds of methods get persimmon cuttings to root with absolutely zero luck including using a cloning machine. One method I've seen used was to wrap a wire around a small branch to cause auxin to accumulate. A cut is made to disconnect most of the cambium, but not all from the tree. They then take a large plastic soda bottle, put it over the branch and fill it with sphagnum peat moss. This is done in the spring and by fall, easily rooting trees (like apples) will produce roots. The problem is that slower to root trees will not have produced roots by winter and will die.
The method that you describe, bends a flexible branch down to or below ground level. Using the wire to accumulate auxin can also be done. Soil is then mounded on the bend. Depending on the region you are in and how deep the ground freezes hard, this gives the branch multiple growing seasons to grow roots. I have not tried this method myself but I have read about it.
Thanks,
Jack