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OCR H446 1.4.2 Trees and hierarchical structures
Part 9 of 14 · H446 1.4.2 · Data structures
A festival programme of categories and activities gives H446 1.4.2 tree vocabulary something concrete to describe. This worksheet holds students to exact terms for the parts of a tree, then makes the point that removing an internal node needs a stated policy, because the structure alone does not decide one.
Students will:
- use root, parent, child, sibling, leaf, subtree and depth accurately under a stated depth convention
- distinguish binary from multi-branch trees and read child-pointer values including absent children
- choose and state a removal policy for an internal node rather than assuming one
- contrast breadth-first and depth-first traversal by the state each one keeps
- design a media-library hierarchy and justify the tree type, one traversal purpose and one removal
Inside: 7 explanation cells, 3 multiple-choice questions, 1 fill-in-the-blanks cell and 3 written answers. 24 marks, about 45 to 55 minutes.
Series: H446 1.4.2 · Data structures, part 9 of 14.
Shared by Coding PathwayVerified teacher
- 14 cells
- About 45 minutes
- CC BY-SA 4.0
- Shared 31 Aug 2026
- Updated 3 Sept 2026
Preview
The whole resource, exactly as a class sees it. Answers and marking are held back.
Trees and hierarchical structures
A festival programme naturally forms a hierarchy of categories and activities. Trees represent parent–child relationships without cycles.
By the end, you will be able to
- use root, parent, child, sibling, leaf, subtree and depth;
- distinguish binary and multi-branch trees;
- traverse, add and remove nodes with stated policy;
- recommend a tree for hierarchical data.
Reactivate: a graph uses nodes and edges.
Read the hierarchy
Festival is the root. Stages and Workshops are siblings. Code is a leaf. The Workshops subtree contains Workshops and all descendants. A binary tree allows each node at most two children; this multi-branch tree allows more.
Worked operation and traversal policy
Adding a workshop attaches a new child to Workshops. Removing a leaf is direct. Removing an internal node needs a stated policy: remove its whole subtree, promote children, or reject until empty. The structure alone does not decide policy.
In an array-backed binary tree, a child field stores another node index; −1 means no child at that particular link. A node is a leaf only when it has no children. Depth-first traversal follows a branch and uses recursive calls or a stack to remember where to backtrack. Breadth-first traversal uses a queue to visit one level before the next.
What does binary tree mean?
- AEvery node always has two children
- BEvery node has at most two children
- CThe tree stores only 0 and 1
- DThe tree has two levels
A binary-tree node has left = −1 and right = 7. Which conclusion is valid?
- AIt is a leaf because one pointer is −1
- BNode 7 must be its parent
- CIt has no left child but does have a right child, so it is not a leaf
- DThe whole tree is empty
Which state mechanism matches the traversal?
- ADepth-first must use a queue; breadth-first must use no state
- BBoth traversals always visit nodes alphabetically
- CBreadth-first follows one branch to a leaf before remembering siblings
- DDepth-first uses recursion or a stack for backtracking; breadth-first uses a queue
Guided vocabulary
For each node, state parent, children and whether leaf. Then give depth with root depth 0. Naming the convention prevents off-by-one disagreement.
Using the diagram, state the root, the parent of Art, the siblings of Code, and all leaves.
Use the displayed hierarchy.
Students type their answer here.
Independent transfer
Design a tree for a school media library with top categories, subcategories and items. Include both a binary or multi-branch choice and a removal policy.
Give at least eight labelled nodes/relationships, justify tree type, describe one traversal purpose, one addition and removal of an internal category.
State what happens to descendants.
Students type their answer here.
Explain why a tree may model the festival hierarchy more clearly than a flat list.
Use relationships and traversal.
Students type their answer here.
Closed-book checkpoint
Complete each sentence from memory. There is no answer bank and correctness is held for teacher review.
Review your responses
Check every response against its command word and the supplied constraints. Strengthen unsupported answers with accurate method, mechanism, state or contextual consequence before submitting.