Hi Vijay,
As per my understanding you want to create a collapse and expand list inside the panel.
Find the components such as “Panel” and “Tree” in the “Component Library” of “AppDesigner” using which the expand/collapse list is created inside the panel.
In the above figure I have created two “Tree” inside the “Panel”.
The below figure shows the “Component Browser” structure for the above output in the “AppDesigner”
Also refer to the "AppDesigner" documentation for more information.