What leader of what country first lit the Christmas tree?

If you mean electrically lit, as opposed to candlelight ( super fire hazard) probably some executive at Con Ed Power and Light was called upon to flip the master switch. there were some real challenges in bringing down the light-heat levels of these bulbs to permit safe usage on trees. it was not solved until l895- whereas Con Ed ( known originally as Edison Lamp Works) was up and running in NY since l879. B y the way in l895, ll0 volts was standardized-still is.