Assuming you mean Milton College in Wisconsin, USA...
There is this category:
https://www.wikitree.com/wiki/Category:Wisconsin%2C_Colleges_and_Universities
It does not yet (as of this writing) include Milton College.
Looking at the subcategories listed there, I think your category would simply be
Category:Milton College
(Note that none of the college or university categories use the name "Graduate", just the name of the college or university.)
Once created, be sure to edit it to add
Category: Wisconsin, Colleges and Universities
To the category page.