Custom Column Creation help

Hi,

Can any one please help me to derive below Type Flag as column from Main Num and Alternate Number based on below logic.

if Main Num not present in Alternate Number list then it's parent
if Main Num is present in Alternate Number and also Alternate Number is present in Main Number list then it's Child- Parent
if Main Num is present in Alternate Number and Alternate Number is not present in Main Number list then it's Child

i have tried below custom column in power query but it's not working for all above three conditions.

 #"Added Custom" = Table.AddColumn(#"Filled Down", "Flag", each if List.Contains(#"Filled Down"[number],[associated number]) then "Parent" else "Child")