What exactly is this, and does it just apply to Tillerson?

I have heard that Rex Tillerson gets some kind of tax benefit if he remains as Secretary of State for at least one year. e.g.

Tillerson has strong financial motive to not quit for a few more months. https://t.co/2bbbaxZ4tI pic.twitter.com/RIyVl11aoQ

— Matthew Yglesias (@mattyglesias) October 7, 2017

Can someone explain to me how that tax advantage works, or give me a link that explains it? Does it apply only to Tillerson, or would it apply to Trump's other cabinet members? (I don't think this explains where the one-year rule comes into play)

I'm wondering if Tillerson will resign when the clock strikes midnight on February 1, 2018 or will we be facing mass resignation in early 2018?