On Linux with AT-SPI2, applications are part of the accessibility hierarchy that has the desktop as it's root object.

However, Qt applications currently don't report any accessible parent.

Steps to reproduce:

1. start any Qt application e.g. the spinboxes example (qt5/qtbase/examples/widgets/widgets/spinboxes/spinboxes)
2. start Accerciser
3. select the Qt application in Accerciser's tree view showing all applications registered via AT-SPI (and their hierarchy)
4. in Accerciser's IPython console, query the parent of the application: 

   In [7]: acc.parent
   In [8]: acc.parent == None
   Out[8]: True 

Actual result:

No parent is reported (s. above)

Expected result:
The AT-SPI desktop object should be reported.

This e.g. works just fine for GTK applications like gtk3-demo:

In [9]: acc.parent
Out[9]: <Atspi.Accessible object at 0x7fbebc3fc1c0 (AtspiAccessible at 0x139d6410)>
In [10]: acc.parent.role
Out[10]: <enum ATSPI_ROLE_DESKTOP_FRAME of type Atspi.Role>