If you want to select only 1 node at a time then use FolderTree.Override.SelectionType property and set it to Single or you want drag and drop functionality also Set it to SingleAutoDrag

in my case, when I selected B by right click, both A and B will be highlighted. How can I make only the current selected node be highlighted?

Thanks.

If you want folder 'B' to be active, set the control's ActiveNode property to reference that node.

Example:
this.ultraTree1.ActiveNode = nodeB;