How can I buy bulk Bitcoin?

As a keen investor in the world of cryptocurrencies, I'm particularly interested in Bitcoin and its potential for long-term growth. However, I'm wondering how I can effectively buy Bitcoin in bulk quantities. Could you elaborate on the steps involved in making such a significant purchase? Are there any specific platforms or exchanges that cater specifically to bulk buyers? Also, I'm concerned about the safety and security of such transactions. What measures should I take to ensure the safety of my funds and investments? Lastly, how can I manage the storage and custody of such a large amount of Bitcoin securely?