Trees and graphs are where many career changers struggle.
Binary Trees: Each node has - children. Know: traversals (inorder, preorder, postorder), height, depth.
Binary Search Trees: Left child smaller, right child larger. search in balanced trees.
Graphs: Nodes with arbitrary connections. Know: BFS, DFS, detecting cycles.
These appear in "medium" and "hard" problems. You need basic understanding but don't need to be an expert for junior roles.
For deep coverage, see Sections - of the Data Structures roadmap.
Career Changer Tip: Focus on BFS and DFS. They solve most tree/graph interview problems.