There is no any Prescribed syllabus to prepare BHU PET entrance Exam. In order to prepare the exam for M.Sc Botany, You can prefer the Graduation syllabus and also you can go through with the previous year question papers to know the level of the questions, You can download the previous year papers with the given below link.

http://bhuonline.in/old-qus-paper-entr.html

Good Luck!