I have a pandas dataframe of two columns A and B as below

Dataframe

I want to print a tree of parent/child relation based on below:

1- If any process in col ‘A’ does not appear in col ‘B’ then it will be a root of tree. In this case process1 and process14 does not appear in ‘B’ so they are the root
2- process1 (root) created process2, process4 and process5 and process2 created process3 and process5 created process6.
3- process14 (root) created process15, process16, process19 and process16 created process17 and process18.

So the desired output should be like below:

|_process1
    |_process2
        |_process3
    |_process4
    |_process5
        |_process6


|_process14
    |_process15
    |_process16
        |_process17
        |_process18
    |_process19

I converted both columns into lists

list1_a = ['process1','process2','process1','process1','process5','process14','process14','process16','process16','process14]

list1_b = ['process2','process3','process4','process5','process6 ','process15','process16','process17','process18','process19]

But I not able to create a good structure which creates this parent/child relation and then I can print out.