I have change the line style to organic in the format topic..dialog box, not still unable to achieve the tapering effect
This is in the Help:
Change the general layout of the map
The General Layout options are
only available if you have the central topic selected. These options apply
to the entire map. You can only set these options in Map View.
Select the central topic.
On the Format tab, click the Object Format dialog launcher. Or, click the Topic Shape arrow and select Format Topic.
On the General Layout tab, choose the desired attributes for the map.
Organic appearance makes the main topic connecting lines look more like hand-drawn lines.
Display shadow adds a shadow to the topic connecting lines and topic shapes.
Main Topic Line Width controls the thickness of lines connecting the central topics and main topics.
Main Topic Spacing controls the spacing between the main topics.
The operation of the Organic Appearance tickbox we had under the General Layout tab up until MM 2018 seemed inconsistent, but the new arrangement is even more confusing.
Having to choose the line appearance not from a dropdown menu specifically for this purpose but instead via a "Thickness applies to" menu is not exactly intuitive. Even then the choices are obscure and the effects depend to some extent on the Line Style selected under the Subtopics Layout tab.
As indicated above, the most "organic" effect comes not from selecting Organic Lines in the Thickness Applies To menu, but instead by choosing Main Topic Line.
However if you have selected curved lines under Line Style than Organic Lines will give you a subtle "reverse organic" appearance, where the lines taper towards the central topic rather than away from it. This doesn't seem to apply however if you choose any of the other line styles.