So confusing! TIER 5 Glasgow

Dear all,
I am desperate. I am a Russian citizen living in Itay since I was little but never asked for EU's citizenship. I was invited to attend a Spring Week in Glasgow (an internship at an investment bank) that lasts 3 days but the bank did not give me a certificate of sponsorship and told me that I am on my own about visa issue.
I am really trying to understand which kind of visa should I ask for and I was suggested TIER 5 (temporary worker) as an unpaid internship is still a job. But when the online procedure asks me for a sub-type of visa (charity worker, creative and sportpeople, government authorized exchange, youth mobility scheme) I am so confused because it's not really a charity work. So what should I do ?
I really pray for someone to help me with this. I really care about this internship but nobody receives calls nor emails about this circumstances.
Thank you for your time!
Sofia

Internship visas like this would have to be supported by BUNAC, I think. They are an organisation that deals with international internship visas.

Why dont you just try for an ordinary visitor visa?