Major Description
When we move an entry, we update all the ascendants up to the root, in order to update the number of descendants.
We can save us a few updates by stopping when we met the common ascendant, because it will have the same descendant number.
For instance, moving an entry from A/B/C/D/xxx to A/B/E/F/xxx will decrement the nbSubordinate counter for C and D, increment it for E and F, but for B, it will remain the same.
Doing so, in this very example, we would save 4 updates, dividing by 2 the number of updates.