Hi Thiago,
Sorry, realy i just only show, how do select father´s tickets. Folow Solution:
1. Build a Query with parent field is not null like the last image.
1.1 Drag and drop ref_num to Object Window
2. Build a second query (add query)
2.1 Drag and drop ref_num field to filters window.
2.3 in list
2.4 select query 1
Good work