Ancalagon
Dusty Dragon
Bear in mind that the actual historical longsword would be covered by 5e's Greatsword category. (Its on the light end of the range and uses more thrusting, but its definitely a two-handed weapon.)
I *completely* disagree, and I will explain to you why.
Can a human use a greatsword, in D&D, with one hand? No. It cannot be done. A gm might allow it with a great penalty, but it's horrible. This does *not* correspond to a historical longsword, where you could do this! It was *better* with 2 hands (and look at that, the damage goes up from 1d8 to 1d10...) but it was quite usable one handed.
What historical sword that is very poor used one handed? The zweihander. Large claymores. The Zhanmadao (tentatively, I am less familiar with that one). THOSE are D&D 2 handed swords, not the longsword.