Your question posits an infinite regress. A logical impossibility .
So
Everything that begins to exist has a cause
The universe began to exist
Therefore the universe has a cause.
Why is it a logical impossibility?
Perhaps what we call ‘reality’ requires no starting point. Maybe it consists of an infinite sequence of Big Bangs and Big Crunches.
Or perhaps all there is is an ungraspable, eternally instantiating, unfathomable Now (since all that we ever get to experience - albeit with a slight time lag in terms of cognitive processing - is the present moment).
Or maybe creationist Christians are wrong and the universe isn’t a few thousand years old. I think it was Bertrand Russell who once suggested that the universe could equally have been created a few moments ago with our seeming memories of a past already implanted.
Moving on, ‘cause and effect’ is a basic notion that we take for granted, one that sustains our sense of our own personal history and that of the wider world. Scientific method is also founded on it, as well as Aquinas’s cosmological argument for the existence of God, which presents Him as a causeless cause of the universe.
But - as the wonderful sceptical philosopher David Hume once pointed out - there is no reason to accept this idea because we never actually see it happen. All we ever perceive is one thing taking place after another, a series of what Hume called ‘constant conjunctions’. We never witness the first event making or forcing the occurrence of the second event. Causes and effects are therefore inferred from events not observed.
But suppose, after all, that there is a ‘causeless cause’ of the universe. If so, that does not entail that the God of classical theism was responsible for its creation. Maybe a team of gods working in tandem did the work, or an evil God (an amusing suggestion ventured by the philosopher Stephen Law).
Right. Now that’s sorted, am off to buy the Christmas edition of Viz Comic.