You can copy the same spell in the ritual book multiple times. But you can already cast a ritual spell multiple times when you have inscribed it once.
Nothing in the feat and no other mechanic prevents you from copying the same spell into your ritual book multiple times.
But most of the time, doing so is a waste of resources because when you have one copy of the spell in your ritual book, you can already cast it as a ritual.
Certain spells have a special tag: ritual. Such a spell can be cast
following the normal rules for spellcasting, or the spell can be cast
as a ritual. The ritual version of a spell takes 10 minutes longer to
cast than normal. It also doesn't expend a spell slot
So you can already cast the spell multiple times when you have it as a ritual. To learn more about rituals, make sure to read the Ritual Section in the Basic Rules.