The standard way when using ordinal arithmetic is:
Take the ordinal 1, which is {{}}.
Replace each element with a ordered pair of the form {{a},{a,b}} with second element being 0 (that is {}).
Repeat with second element 1.
Take a union.
Take find the ordinal with this order.
Overall:
otp({
{{{}},{{},{}}},
{{{}},{{},{{}}}}
})
Or simplified
Although that's fairly easy to write. It's hard to calculate, if you calculate the brackets first.
I saw somewhere that someone had decoded how an AI had learnt to do basic arithmetic. And it appeared to be using a massive expression containing lots of sin & cosines to do basic addition
\tan(\pi/4) + 1/42 \int_{-7\ln 6}^\infty \exp(-x/7) \dd{x}