Click BMS on the Options menu of the IDE to display this dialog box as shown in the figure below.
The default settings on this dialog box should enable you to edit an existing BMS macro file or create a new mapset.
See the popup help for each field for a description of what it does - click ? in the title bar, then click the field.
You can see the View page of this dialog box in the figure below.
Here you can specify whether the tree view shows macro entries or copybook entries.