Write SQL query to solve given problem: Find the university from which the professor who advised most undergraduate students graduated.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T1.graduate_from FROM prof AS T1 INNER JOIN RA AS T2 ON T1.prof_id = T2.prof_id INNER JOIN student AS T3 ON T2.student_id = T3.student_id WHERE T3.type = 'UG' GROUP BY T1.prof_id ORDER BY COUNT(T2.student_id) DESC LIMIT 1