A user describes a tree or a set of trees in a table, and a system generates a data structure corresponding to the tree or the set of trees on memory in accordance with the description. The table has one or more columns in which for each node, attributes given to the node are entered. The system interprets the table; allocates a memory area to each of the nodes, sets data on the attributes given to the node; and generates pointer data indicating the connections of the memory areas. The hierarchy of the nodes and the sequence of nodes linked immediately below the same node are determined on the basis of the sequence of rows corresponding to the nodes and levels assigned to the nodes in the table.