High demand+ bitcoin scarcity
Not limited to this, but
the need for Bitcoins is increasing with the increase in total users who are adopting it as well as the fear of hard fork is now settled as things have gone south for Bitcoins after Bitcoin cash got dumped by everyone and no support is being shown and the coin isn't entertained much. Thanks BCH, you gave Bitcoins this boost which we have all been waiting for.
OP, the bubble didn't start yet as you are yet to see the whole picture from now onwards.
There is no sign of increased adoption - the number of transactions every 24 hours has held steady at about 250,000 for months now. It has not been increasing. I think this is a pure speculative bubble.