Hi soober,
We have Modified the sample based on your requirement. In the Expand Collapse sample, a new node can be added to the DiagramPage by Drag and Drop the Symbol from SymbolPalette on to any of the particular Node in the Page. The new node can be added as children of that particular Node. Please refer to the Attachment
Please let us know if you have any further queries and we will be happy to help you out.
Regards,
Ramya
ExpandAndCollapseDemo_3a5d1d31.zip