parent any node (except the roothas exactly one edge running upward to another node the node above it is called the parent of the node child any node may have one or more lines running downward to other nodes these nodes below given node are called its children leaf node that has no children is called leaf node or simply leaf there can be only one root in treebut there can be many leaves subtree any node may be considered to be the root of subtreewhich consists of its childrenand its children' childrenand so on if you think in terms of familiesa node' subtree contains all its descendants visiting node is visited when program control arrives at the nodeusually for the purpose of carrying out some operation on the nodesuch as checking the value of one of its data fields or displaying it merely passing over node on the path from one node to another is not considered to be visiting the node traversing to traverse tree means to visit all the nodes in some specified order for exampleyou might visit all the nodes in order of ascending key value there are other ways to traverse treeas we'll see later levels the level of particular node refers to how many generations the node is from the root if we assume the root is level then its children will be level its grandchildren will be level and so on keys we've seen that one data field in an object is usually designated key value this value is used to search for the item or perform other operations on it in tree diagramswhen circle represents node holding data itemthe key value of the item is typically shown in the circle (we'll see many figures later on that show nodes containing keys