Forgotten Realms: Mjeledi, a magic whip for D&D 5th Edition

In my Forgotten Realms game, I'm creating some magic items to seed my campaign with:

A gift from the treant, Kloryfon, to the Tong tribe in Chult.  The Tong have always allowed their craftiest warrior to wield their most prized trophy.

MJELEDI

Magic weapon (whip), rare (requires attunement)

You gain these benefits while wielding this magic item:

• You gain a +2 bonus to attack rolls and +1d4  to damage rolls.

• When you roll a 19-20 on your attack roll, you may knock your target prone.