Ok, first of check this article out here, you should be able to find everything you need to create what you need.
Now here is all formulas per every level in your example
Level 1
=IF(ISERROR(VALUE(SUBSTITUTE(OFFSET(A1,-1,0,1,1),".",""))),1,IF(ISERROR(FIND("@",SUBSTITUTE(OFFSET(A1,-1,0,1,1),".","@",1))),VALUE(OFFSET(A10,-1,0,1,1))+1,VALUE(LEFT(OFFSET(A1,-1,0,1,1),FIND("@",SUBSTITUTE(OFFSET(A1,-1,0,1,1),".","@",1))-1))+1))
Level 2
=IF(ISERROR(VALUE(SUBSTITUTE(OFFSET(A2,-1,0,1,1),".",""))),"0.1",IF(ISERROR(FIND("@",SUBSTITUTE(OFFSET(A2,-1,0,1,1),".","@",1))),OFFSET(A2,-1,0,1,1)&".1",LEFT(OFFSET(A2,-1,0,1,1),FIND("@",SUBSTITUTE(OFFSET(A2,-1,0,1,1),".","@",1)))&IF(ISERROR(FIND("@",SUBSTITUTE(OFFSET(A2,-1,0,1,1),".","@",2))),VALUE(RIGHT(OFFSET(A2,-1,0,1,1),LEN(OFFSET(A2,-1,0,1,1))-FIND("@",SUBSTITUTE(OFFSET(A2,-1,0,1,1),".","@",1))))+1,VALUE(MID(OFFSET(A2,-1,0,1,1),FIND("@",SUBSTITUTE(OFFSET(A2,-1,0,1,1),".","@",1))+1,(FIND("@",SUBSTITUTE(OFFSET(A2,-1,0,1,1),".","@",2))-FIND("@",SUBSTITUTE(OFFSET(A2,-1,0,1,1),".","@",1))-1)))+1)))
Level 3
=IF(ISERROR(VALUE(SUBSTITUTE(OFFSET(A3,-1,0,1,1),".",""))),"0.0.1",IF(ISERROR(FIND("`",SUBSTITUTE(OFFSET(A3,-1,0,1,1),".","`",2))),OFFSET(A3,-1,0,1,1)&".1",LEFT(OFFSET(A3,-1,0,1,1),FIND("`",SUBSTITUTE(OFFSET(A3,-1,0,1,1),".","`",2)))&IF(ISERROR(FIND("`",SUBSTITUTE(OFFSET(A3,-1,0,1,1),".","`",3))),VALUE(RIGHT(OFFSET(A3,-1,0,1,1),LEN(OFFSET(A3,-1,0,1,1))-FIND("`",SUBSTITUTE(OFFSET(A3,-1,0,1,1),".","`",2))))+1,VALUE(MID(OFFSET(A3,-1,0,1,1),FIND("`",SUBSTITUTE(OFFSET(A3,-1,0,1,1),".","`",2))+1,(FIND("`",SUBSTITUTE(OFFSET(A3,-1,0,1,1),".","`",3))-FIND("`",SUBSTITUTE(OFFSET(A3,-1,0,1,1),".","`",2))-1)))+1)))
Level 4
=IF(ISERROR(VALUE(SUBSTITUTE(OFFSET(A4,-1,0,1,1),".",""))),"0.0.0.1",IF(ISERROR(FIND("`",SUBSTITUTE(OFFSET(A4,-1,0,1,1),".","`",3))),OFFSET(A4,-1,0,1,1)&".1",LEFT(OFFSET(A4,-1,0,1,1),FIND("`",SUBSTITUTE(OFFSET(A4,-1,0,1,1),".","`",3)))&IF(ISERROR(FIND("`",SUBSTITUTE(OFFSET(A4,-1,0,1,1),".","`",4))),VALUE(RIGHT(OFFSET(A4,-1,0,1,1),LEN(OFFSET(A4,-1,0,1,1))-FIND("`",SUBSTITUTE(OFFSET(A4,-1,0,1,1),".","`",3))))+1,VALUE(MID(OFFSET(A4,-1,0,1,1),FIND("`",SUBSTITUTE(OFFSET(A4,-1,0,1,1),".","`",3))+1,(FIND("`",SUBSTITUTE(OFFSET(A4,-1,0,1,1),".","`",4))-FIND("`",SUBSTITUTE(OFFSET(A4,-1,0,1,1),".","`",3))-1)))+1)))
Of course there may be some other way, but this works too.
Let me know if you have problem with this.