It's a way of visualizing and notating the process of finding the prime factorization of a given composite number. Some people can do it in their heads, but for most of us, it's easier to write it down.
Prime numbers don't have factor trees. So if you can create a tree, your number's composite.
If completed correctly, the bottom branch of a factor tree will be the prime factorization of the number at the top.
factor tree of 216
IT IS PRIME there is no factor tree
Factor tree of 204
The factor tree of 50:5025,25,5,25025,25,5,2
21
83 is prime. No tree.
The prime factor tree of 280 is:140,270,2,235,2,2,27,5,2,2,2
Factor Tree of 20: ........20 ......../ \ .......4 5 ....../ \ .....2 2
A tree.
The factor tree for 148: 148 74,2 37,2,2