Indeed, it is deceptive to marry a second wife without the first wife knowing about the second (or without the second wife knowing about the first). However, scholars consider such a marriage would ordinarily be valid. Scholars acknowledge this, e.g.:
Lying and deception are, without doubt, two of the major sins and from among the enormities (kaba’ir). But again, they are independent sins, and do not invalidate a man’s second marriage.
Basically a marriage can meet the requirements of a valid marriage. JustAskIslam lists these requirements as:
The conditions of marriage are four:
The presence of the couple
The presence of the woman’s guardian
Two male, Muslim witnesses
Generally, having more than one wife itself is discouraged (let alone doing so deceptively):
It is generally not advisable for men to marry more than once in our times, because of the harm and wrong that inevitably results, unless there is a genuine need.
And, even in Muslim-majority countries, there's also non-sharia laws which inhibit polygamy, e.g., in Pakistan:
A Pakistan court on Wednesday ruled against a man who had remarried without his first wife’s permission in a landmark verdict that was applauded by women’s right activists. ... Judicial magistrate Ali Jawwad Naqvi announced the verdict in a Lahore lower court, ordering the man to serve a six-month jail term and pay a fine of 200,000 Pakistani rupee ($1,902.95).
Pakistan makes landmark ruling against man for second marriage, Reuters, 2017
If having a co-wife is not desired, conditions on monogamous marriage can be added to the marriage contract: Can a man have up to four wives? It is also possible for the potential second wife to say "I'm not marrying you without the permission of your first wife".