Is mega backdoor roth considered Roth IRA?

My employer's 401K let me contribute (35K) after tax dollars through an in-plan conversion for the mega backdoor roth. Does this mean my 401K contain both taxes and untaxed contributions? Does the after taxed contributions in this account considered a Roth IRA account that I need to report on TurboTax? Are they the same thing? I received a 1099-R form from my broker for this 35K (box 5) contribution.