Where does “jeślik” come from?

jeślik (Polish) comes from Polish jeśli, from Old Polish jestli, from Czech být, from Old Czech býti, from Proto-Slavic *byti, from Proto-Balto-Slavic bū́ˀtei, from Proto-Indo-European bʰuH- — to become, grow, appear.

Ancestry of “jeślik”, step by step

StepLanguageWordMeaning
1Polishjeśliintroduces a real conditional clause; if
2Old Polishjestliintroduces a conditional; if
3Czechbýtto be; Jel jsem do Prahy. ― I went to Prague;...
4Old Czechbýtito be
5Proto-Slavic*byti—
6Proto-Balto-Slavicbū́ˀteito be
7Proto-Indo-EuropeanbʰuH-to become, grow, appear
Every word from Proto-Indo-European bʰuH- →Every word from Proto-Balto-Slavic bū́ˀtei →Every word from Proto-Slavic *byti →