no, fellah. read again.
your family tree crosses itself many times.
meaning that some of your ancestors are represented as "20th-great grandfather" through multiple lines, essentially creating "virtual" duplication where no real duplication has occured.
shall I generate a chart to graphically explain this process?
No, I understand, like 2 and 3rd cousins marrying they have the same gg-ggg-grandfather. But still.