How can I select the true expansion?

 How can I select the true expansion?

I have a series expansion which gives two results.

Series[-(1/  Sqrt[-1 + x + x z1^2 \[Chi]^2]) , {x, 0, 1}] /. y -> x  

I want only the series which is true. I know I can do by using Assumptions or Assuming by discarding the other. But I want the other way i.e. Mathematica should pick the true one.

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