In the example below, node b from the previous example was replaced by a missing node. Http://medicinanaturale.pro/asshole-63/dawn-bates-escort-18981.php start with a root node r which has two children, node a and node b. If you later want to make more complex trees, you can also use TikZ styles in just the same way.
Ok thank you very much for the comment. The thing is that I am doing a Venn diagram just as the one in. In the example below, I increased the line thickness to thick and changed nodes to a minimum size of 0.
9.3. Growing a tree
Which is the number  and as you can see the reference goes way out trees in latex margins. The code I am having now is using the trees library: Declare the nodes and children in the tree hierarchy. For simple trees, however, forest is very simple. In the example below, node b from the previous example was replaced by a missing node.