>The short answer is that the "misspelling" is on purpose, done to differentiate Treasury bonds from the plural for the Department of Treasury, though I'm not sure why you'd ever need to pluralize that. In any event, a number of business news organizations, including CNBC, use the "Treasurys" spelling.
Colloquially known as the US Treasury, which could conceivably be pluralized as Treasuries.
Some other reasons for the alternative spelling:
In many style guides, proper nouns ending in -y are pluralized as -ys, not as -ies. For example, Casey plural would be Caseys, not Casies. Treasury, referring to the type of institution is not on its own a proper noun, but "Treasury", the name of the security emitted by the US Treasury, might be.
Another reason for the alternative spelling is in financial settings, the plural of Treasury (notes, bonds, etc.) is abbreviated as Tsys. Treasurys is a reasonable "backronym" for that.
>The short answer is that the "misspelling" is on purpose, done to differentiate Treasury bonds from the plural for the Department of Treasury, though I'm not sure why you'd ever need to pluralize that. In any event, a number of business news organizations, including CNBC, use the "Treasurys" spelling.