If 'Tag tree at placement' has been selected, a label is displayed at the centre of each instance recording the Unique Reference of each Existing Tree.
To display tags after placing Existing Trees, use the Place Tag(s) option from the ribbon.
Pick Place Tag(s) to display a tag at the centre of the Exsting Tree (below - left).
Pick With Leader to display a tag with a leader line to the Exsting Tree (above - right).