Multiple parents for bubble
Currently, a bubble can only have one parent (connected with a parent line). There are a couple of things you can try to achieve a desired layout.
Connecting lines
Use connecting lines to create a structure of multiple parents. For details on how to create connecting lines, see our help page Connecting Lines
Note: You can update connecting lines to remove arrows.
Tree layout
Another option would be to use a Tree layout in an upward direction. This will give you the following look:
To achieve this, you can change the layout of the child bubble like so:
