When splitting bones, there is a nesting option.
check for nesting
If you divide 'bone' into 3, it is created as bone, bone2, and bone3.
without checking nesting
If you divide 'bone' into 3, bone1, bone2, and bone3 are created.
Even when I checked the nesting when dividing the bones,
We want the number1 to run on the first bone of the divided bone as well.