Back in August, 2017, I visited the biggest synagogue in Budapest, the Dohány Street Synagogue, and was told the following story by the tour guide:

During WWII there were approximately 70,000 Jewish people put into a Ghetto. The Hungarian government made a deal with Hitler that in exchange for free transportation of the Nazi army through Hungary, these Jewish people would not need to be sent to the concentration camp. However, were these people safe? No. The Hungarian army rounded up dozens of people at a time, brought them to the Danube on boats, and shot them. They then pushed the dead bodies into the river.

The tree pictured above is in the courtyard of the Synagogue, is called the Tree of Life, and the leaves (as shown below) are engraved with the names of Jewish people who passed away.

Unfortunately, my computer crashed and I lost all of my other photos of inside the Synagogue.  However, I would definetely recommend to visit.