Imagine if you had a big family with lots of brothers, sisters, cousins, and grandparents. Now, imagine that you were all the leaders of a country called the Byzantine Empire a long, long time ago.
At the top of the family tree were the emperors, who were like the kings of the Byzantine Empire. They ruled over the whole empire and made important decisions about everything from wars to taxes to laws.
There were lots of emperors throughout history, but they all came from the same family. The very first emperor, named Constantine, started it all in the year 306. After him, his son, and his grandson became emperors too.
As time went on, there were lots of emperors who were related to each other. Sometimes, fathers and sons were both emperors. Other times, uncles and nephews or cousins were emperors too.
It might seem a little bit confusing, but the family tree of Byzantine emperors is just like any other family tree. There are lots of branches that go in different directions, but they are all connected to the same trunk. And just like in your family, some of the branches might be bigger or more important than others, but they wouldn't exist without the trunk.