Bitcoin. Understaing the Value of shares/currency/market

Hello dear sir, I need some help in understanding the value of smth. In the market we know that there are bulls and bears, and when people buy the price of the share is increasing, when people are selling the price is decreasing. OK. But help me understand that using the example of Bitcoin. We say thats a currency, so the Forex rules apply. Right? I want to understand, why the bitcoin price is increasing so rapidly? Only because people expecting higher prices in future? Any value backed-up behind this? Any collapse can happen? Whats the difference from Financial Pyramid? Will much appreciate to get some expert advice on it with explanations.