Problem kicking my ass – EXCEL sort issue

I cannot find any way to fix this problem. I have hundreds of numbers in an ‘outline’ type format and I cannot get a correct sort no matter what I try. I have tried every format possible. Does anyone know a work around?? Here is what I want to achieve:
1.1
1.1.1
1.2
1.3
1.3.1
1.4.2
1.5
2.1
8.5
8.5.1
8.5.10
12.1
12.3.10
Here is what I get:
3.10
4.20
8.40
10.10
12.20
10.2.2
12.1.1
12.3.10
3.6.1
3.6.10
3.6.2
8.5.10
8.5.15
8.5.7
9.3.2