Grouping and Ungrouping Layers
You can also nest layers together in a group using the Group command. You can group
layers that appear in the same group, or you can group groups that are nested at the
same level relative to the hierarchy of your project. You cannot group groups that appear
at different levels.
To group selected layers together, nesting them in a group
Select all layers or groups you want to group together.
Choose Object > Group (or press Command-Shift-G).
A new group is created and is numbered incrementally based on the number of groups
you’ve created so far. The layers or groups you selected are nested in the group.
Groups of nested layers or groups can also be ungrouped, which deletes the containing
group and moves objects and layers in it up the group hierarchy.
To ungroup nested layers
Select the group containing the nested layers or groups to ungroup.
Choose Object > Ungroup (or press Command-Option-G).
Note: You cannot ungroup groups that are at the root (project level) of the Layers list