When setting up a tree map, what must you first add to the workbook?

When setting up a tree map in a workbook, the initial step involves adding a source worksheet. This is essential as the source worksheet contains the foundational data that the tree map will visualize. The tree map requires input data structured in a way that can effectively represent hierarchical relationships, which typically originates from the source worksheet. By starting with a source worksheet, users can ensure they have the correct data landscape necessary for constructing the visual representation of that data.

Other types of worksheets mentioned, such as composite or linked workbooks, do not serve as the foundational step for creating a tree map, as their function often pertains to organizing or linking data rather than providing the initial dataset for visualization. The diagram worksheet is also dependent on pre-existing data, which must be sourced from the source worksheet. Therefore, the source worksheet serves as the critical starting point for the creation of effective visualizations like tree maps.