Principles for Drawing Tree Diagrams
Borrowing terminology from genealogical trees, the nodes below another node are sometimes called the children of that node. A node that has children is a parent node. Just as with people, parent nodes can themselves be children of other parents. If we need to talk about nodes that are children of children, we call them descendants. Unlike genealogical trees, however, it is important to note that while a node may have several children, it only has one parent. Also, each line should connect to one child node. Do not show two edges connecting to a single word.
Further, you should always space out your nodes so that edges do not cross one another. This practice is merely for visual clarity. In principle, there's no reason why the lines must never cross.
Sometimes, we will not want to analyze a sentence completely. Initially, we will lack the knowledge to analyze everything in a sentence. Later on, with more complex sentences, we may choose to ignore details that aren't relevant to our purpose. In these cases, we will indicate an unanalyzed constituent by using a triangle.
An unanalyzed constituent
 Tree diagrams can also be drawn under the sentence, although in this course we will follow the more common practice.