The TreeView_GetPreviousNode() function returns the ID of the preceding sibling for the specified node.
TreeView_GetPreviousNode(tree_view_field, node_ID)
• tree_view_field – The tree view field containing the specified node.
• node_ID – A long integer specifying the ID of the node whose preceding sibling will be returned.
A long integer containing the node ID of the preceding sibling of the specified node. If the specified node has no preceding sibling, TV_NODEINVALID is returned.