Which of the following is NOT a type of linear data structure?

A tree is classified as a non-linear data structure, whereas a queue, array, and stack are all linear data structures. In linear data structures, elements are arranged in a sequential manner, allowing for a single level of hierarchy where each element has a unique predecessor and successor, making operations like traversal straightforward and predictable.

In contrast, a tree organizes data in a hierarchical manner, where each node can have multiple children, leading to a branching structure. This allows for more complex relationships between data elements and enables efficient searching, inserting, and deleting operations in certain contexts. The hierarchy also means that not all nodes are on the same level, which breaks the linearity characteristic essential to queues, arrays, and stacks.

Thus, recognizing the distinction between linear and non-linear data structures is key, and this understanding clarifies why a tree does not fit into the category of linear data structures.