How many levels is there in security clearance in the government?

There are two kinds of clearance: Secret and Top Secret. There used to also be a Confidential clearance, but they finally figured out Confidential and Secret clearances require the exact same investigation so now it's just Secret and TS.

Now here's where it gets fun: Compartmented Information. Compartmentalization is the process of separating out information and granting clearances only to trustworthy people who need to work with that information. Maybe there is the need for intelligence on bacon. We'll call it BACINT. And OMG if our ultra secret BACINT got into the enemy's hands it would cause grave and irreparable damage to the nation's security. So they create a compartment for BACINT and call it GRANITE. Now, any time you report BACINT (say, to report that Smithfield Ham Shop in Smithfield, NC, has some really tasty bacon) you have to write SECRET GRANITE on it, and the computer that processes all the reports will know to only send SECRET GRANITE reports to authorized BACINT consumers.
There are two kinds of clearance: Secret and Top Secret. There used to also be a Confidential clearance, but they finally figured out Confidential and Secret clearances require the exact same investigation so now it's just Secret and TS.

Now here's where it gets fun: Compartmented Information. Compartmentalization is the process of separating out information and granting clearances only to trustworthy people who need to work with that information. Maybe there is the need for intelligence on bacon. We'll call it BACINT. And OMG if our ultra secret BACINT got into the enemy's hands it would cause grave and irreparable damage to the nation's security. So they create a compartment for BACINT and call it GRANITE. Now, any time you report BACINT (say, to report that Smithfield Ham Shop in Smithfield, NC, has some really tasty bacon) you have to write SECRET GRANITE on it, and the computer that processes all the reports will know to only send SECRET GRANITE reports to authorized BACINT consumers.