Iron, citric acid and their ions
This example depicts the relationship between the element Iron) and its diverse ions, Ferrous Ion and Ferric Ion.
It also shows Ferric Citrate, a combination of two ions - Citrate (a Citric Acid ion) and Ferric Iron, forming a tree structure with two roots.
All other substances related to Iron or citric acid are omitted since they would not add to the value of the example.