KYIV, Ukraine—Former Ukrainian President Petro Poroshenko on Monday returned to Ukraine to face court on treason charges he believes are politically motivated. At the Kyiv airport, where he arrived on a flight from Warsaw on Monday morning, Poroshenko was greeted by several thousand cheering supporters. Some carried banners reading “We need democracy,” and “Stop repressions.” From the airport, Poroshenko headed straight to court, which was to rule on whether to remand him in custody pending investigation and trial. After hours of proceedings, the court adjourned until Wednesday afternoon. A prosecutor has alleged that Poroshenko, owner of the Roshen confectionery empire and one of Ukraine’s richest businessmen, was involved in the sale of large amounts of coal that helped finance Russian-backed separatists in eastern Ukraine in 2014–15. Poroshenko’s assets have been frozen as part of its investigation into the allegations of high treason. The former leader of Ukraine faces up to …