You can use the Tree Control option available in the Display section of the Mask Editor to create the hierarchical list of data in mask dialog box.
Consider a scenario in which you want to create a parent-child hierarchy on a mask dialog box as shown here:
To do so,
Right-click a block and in the content menu click Mask > Create Mask or Mask > Edit Mask.
In the Parameters & Dialog pane, click Tree Control from the Display section.
In the Property editor section, specify these in the Tree Items field:
{ 'Node1', {'ChildNode1', 'ChildNode2'}, 'Node2', {'ChildNode1',
'ChildNode2'}, 'Node3', {'ChildNode1', 'ChildNode2'}, 'Node4', {'ChildNode1',
'ChildNode2'}}
Click Apply.