Advait is a complex topic to understand. There is an example to understand this. Dashrathi Ram, Raghuveer Ram & Ikshvaku Vanshaj Ram is referring to same Ram.

First Ram shows the expansion of his family after Dashrath. Second shows after Raghu & Third shows after Ikshwaku and when we move forward we reach to manu and it ends after that. It is Advait.

Srishti is Sañcara Marga. Mukti is pratisañcara marga. In sañcara marga we move towards many marga from one. This is way of science.

In Pratisañcara marga we move towards one from many.

This is a way of Gyana, Advait is Gyana marga and dvait is way of science.

Both are incomplete without each other. That's why Bhagwana has said.

"ज्ञानं तेsहं सविज्ञानमिदं वक्ष्याम्यशेषतः।
यज्ज्ञात्वा नेह भूयोsन्यज्ज्ञातव्यमवशिष्यते।"

Their existence depends on each other.

That's why shankar Bhagwatpad has also said.

न एकोsहं यत् द्वितीयं कुतः स्यात्।"

Definition of one is!

"एक इता सङ्ख्या। इता अनुगता सर्वत्र या सङ्ख्या सा एक।"

Saptrishi