Where does “ести” come from?

ести (Macedonian) comes from Proto-Slavic estь, from Proto-Balto-Slavic *esti, from Proto-Indo-European *h₁ésti.

Ancestry of “ести”, step by step

StepLanguageWordMeaning
1Proto-Slavicestьestь; third-person singular present active...
2Proto-Balto-Slavic*esti—
3Proto-Indo-European*h₁ésti—
Every word from Proto-Indo-European *h₁ésti →Every word from Proto-Balto-Slavic *esti →Every word from Proto-Slavic estь →