Equating personal identity to material existence is part of why the Cosmological Argument is fallacious.

One of many unproven concepts that the CA is predicated upon is the idea that the universe "began to exist" which is purely speculative. We have no knowledge that suggests at one point the matter and energy which constitutes the universe simply wasn't there, and then was.

When advocates for Kalam/Cosmological Argument argue on behalf of this point they often relate the notion to personal identity. At one point this tree began to exist, therefore things begin to exist.

This is a fallacy of equivocation. The personal identity of the arrangement of matter we call a "tree" began at some point, but the particles and energy which constitute its existence did not suddenly appear.

There's no evidence that matter or energy ever "began to exist" which makes the cosmological argument a random guess. Some have argued that it is "probably true" but that's nothing more than an intuitive gut feeling, because the idea of perpetual existence is difficult for us to imagine, but we don't have any way of determining the likelihood of this, so anyone asserting it's probability is just believing what they want to believe, with complete disregard for the truth.