Generally with an org chart of this scale I would recommend using a separate program. Microsoft Visio is a good one and provides some better tools to be able to construct an org chart containing this many elements.

Your other option if you really want to use a program from the Office suite is to possibly use PPT to create your main org chart showing your Main branches and then use hyperlinks to link each "branch" through to a different slide which would have the rest of the hierarchy in more detail. I'm attached a sample file so you can see what i mean (I've only hyperlinked items 1, 2 and 3).

Hope this helps.

Attached Files

Linked Org Chart.pptx (101.8 KB, 37 views)