I think you are referring to this in the Beginning with the basics Tutorial:
"As a consequence, the bar chart above the treemap does not display all values at the same time. Therefore, it has a mini chart below the bar chart, which shows a miniature of the full chart. The mini chart has a scroll bar that can be used for navigation."
A treemap does not contain a mini chart, but a bar chart does. The quote in the tutorial is correct as such, but I think the wording could be improved to make it clearer that the mini chart is part of the bar chart.