Per Derksen, the Proto-Indo-European root is reconstructible as *teyH- or *teh₁y-, but neither of them can be clearly linked to non-Slavic words. The PIE suffix *-sk- is also present. Per Vasmer and Chernykh, possibly related to *těsto(“dough”), which may be connected with Old Irishtóis-renn, táis(“dough”), Old Englishþǣsma(“leaven”).
Chernykh, P. Ja. (1993) “ти́скать”, in Историко-этимологический словарь русского языка [Historical-Etymological Dictionary of the Russian Language] (in Russian), 3rd edition, volume 2 (панцирь – ящур), Moscow: Russian Lang., →ISBN, page 245
Derksen, Rick (2008) “*tìskati”, in Etymological Dictionary of the Slavic Inherited Lexicon (Leiden Indo-European Etymological Dictionary Series; 4), Leiden, Boston: Brill, →ISBN, page 494
Vasmer, Max (1964–1973) “ти́скать”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress