1. This latest scandal in the government is only the tip of the iceberg. I’m convinced that there is much more corruption than what has been uncovered so far.
2. The police arrested the man they thought was guilty of the robbery. While they had him in jail, they began to uncover information that linked him to many of the robberies that had taken place over the last few years. This latest robbery was just the tip of the iceberg.

The expression suggests that while only the top of an iceberg may be visible, the larger and more dangerous portion of it is hidden from view under the water.