PROBLEM:
Suppose I have a workbook with the following sheets:

USA-north
USA-south
USA-east
USA-west
USA-west-region1
USA-west-region2

CAN-north
CAN-south

QUESTION:
Is there any way to display a "collapsable tree view" of the sheets?
(in a side panel that occupies the entire left side of the GUI, similar
to what you would see in msft windows "explorer tree view"). It would
be nice to have a view where the topmost 'nodes' of the tree would be
USA and CAN which are collapsable and expandable to reveal and
hide the various child nodes associated with them.

RATIONALE:
The reason for this request is that this option (if available) would
help
to visualize the data in the sheets more easily as well as avoid the
effect
of 'runaway spreadsheet tabs' that scroll off the side of the screen at
the
bottom. In other words, a collapsable "show/hide" tree view would make
it easier to navigate the various subgroups of spreadsheet tabs.

Absent availability of this feature, is there an alternative approach
anyone
has found, assuming I am not the first person in the world to think of
this
idea?