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See, for example, here:Where can I see the high energy SM Lagrangian?

https://en.wikipedia.org/wiki/Electroweak_interaction#Lagrangian

As I understand it, it isn't, because before EW symmetry breaking, the Higgs field is not a single scalar field. It's a complex SU(2) doublet, and a direct quadratic mass term would break SU(2) gauge invariance.A quadratic term of Higgs field is allowed.