Tree structure + node

Tree structure ：

The tree structure is like a family tree , Everyone is a node in the tree structure .

Computer directory also belongs to tree structure .

The relationship between nodes

The root node ： Each tree structure has a node without a parent , It is called the root node .

Parent node ：A yes A2 The father of ,A2 yes A2-1 The father of .

Child nodes ：A2-1 yes A2 The children of ,A2 yes A The children of .

Peer relationship ： Nodes with the same parent are siblings ,A1 and A2 and A3 Is peer relationship , however A2-2-1 and A2-2-2 Not at the same level , There is no same parent .