You can hierarchically group any objects both in rows and in columns.
Procedure
Open a matrix model.
Right-click the object that you want to position below another object in a hierarchy. The objects must be arranged directly below or beside each other.
Click Down one level.
For a row, the object is grouped hierarchically below the object that is placed directly above it. For a column, the object is grouped below the object that is placed directly to the left of it. The row or column can be reduced to the top level of the hierarchy by clicking it, that is, the subordinate rows or columns are hidden.
Tip
Select adjacent objects by holding down the Shift key and clicking the first and last object.
You can extend or reduce your selection using the arrow keys.