You can change the horizontal text topic to vertical text topic.
At first, select a topic, then follow "MindMap" tab -> "Add Topics" group -> "Text" feature. (or drop down the "Text" menu, click "Vertical Text" item). The topic text will be rotated to vertical.
It also can restore to horizontal text from vertical text.
Drop down "Text" menu, click "Horizontal Text" item to rotated back the text to horizontal.