Hi Amirtharaj,
Thank you for using Syncfusion products.
MoveUp command in the sample removes selected item from parent only if it succeeds, but subitems are added to new node without any validation. For the failed MoveUp cases, items will not be removed from parent but subitems are added to new node. This causes exception because the item is already a child of another element. We have modified the sample to add subitems in new node only if the MoveUp command succeeds. You can download the modified sample from following link:
Sample:
TestGUI-ModifiedRegards,
Jessie