All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If there is no previous contract between you and your first wife or her guardian that prevents you from second marriage, and you do not apprehend legal punishment that harms you physically or financially, then you may marry a second wife even in secret. But know that the consent of the guardian of the woman and presence of two trustworthy witnesses are compulsory conditions for the validity of the marriage.
Whenever the above conditions are met, the marriage will be valid according to the preponderant opinion of the Muslim scholars.
Allah knows best.