When people draw a diagram by hand, you often see that nodes are connected in a tree-like fashion. In TCM it is quite difficult to draw this because you have to edit the diagram as a graph. In the TCM diagram editors, each line should connect two node shapes; a line cannot connect to another line. The only way to draw something that looks like a ``fork'' is to draw partially overlapping segmented lines. But an even number of lines that overlap in the drawing area becomes invisible, due to the fact that figures are drawn in so-called ``exclusive-or'' mode (see also question A.38). However in PostScript, overlapping lines are visible. As another option, if that is allowed in the diagram technique, you can use a small black dot or another small shape as the junction of the tree.
The tree editors have a special `forked tree' mode where the branches are drawn as a fork. You can not edit the tree in this mode, that is only possible in the `editable graph' mode.