I want to collect bulk data from a website
or http://www.educationboardresults.gov.bd/
for each student of a certain range of roll.
I want to store this data in a Excel file spreadsheet/database.
To do this task manually is very difficult.
Is there any free software/tools to collect this data automatically?
Definitely not Unity 
You would need to do something called web scraping. There is software to speed up the process, but to gather information from a specific site you will have to write it yourself. Essentially you need to write a program that gathers information under specific HTML tags, cycles through the options over and over again, then saves it to a file format. Look up tutorials on something like Selenium. Disclaimer, websites usually don’t want you scraping from them.