A factor tree isn't complete until all the factors are prime. If any of the factors are composite, you know the factor tree is not complete.
All factors of a number
NEVER! A factor tree is strictly division. Factors at the end of a factor tree should all be whole numbers.
multiple all factors together
117 39,3 13,3,3
It doesn't matter what factors you select to start a factor tree. The only thing that matters about completing it is that all the factors are prime.
In doing the factor tree, you can start with any two factors of the given number. These factors maybe prime or composite. But the resulting factors in the factor tree should always be prime numbers. It means that you have to continue factoring unless you ended up with all prime factors.
It's not where you start, it's where you finish. It doesn't matter what factors you select to start a factor tree, as long as all the factors are prime when you finish.
Use a factor tree. 221 13,17 All the factors are prime. 13 x 17 = 221
all factors of 130 are 1, 2, 5, 10, 13, 26, 65, 130
15 and 30 are factors of 60. The factors of 60 include the factors of 15 and 30. 45 is not a factor of 60.