Flash CS4 Professional.
presetItem.level
Read-only property: an integer that specifies the level of the item in the folder structure of the Motion Presets panel. The Default Folder and Custom Presets folder are level 0.
The following example shows that the first item in the Motion Presets panel is level 0 and the second is level 1:
var presetItemArray=fl.presetPanel.items;
fl.trace(presetItemArray[0].level);
fl.trace(presetItemArray[1].level);