Given a tree-like computational data structure, something where every entity (except for the root entity) has exactly one parent and may have any number of children (for example, the internal structure of an XML file). How do I say correctly: You can click this button to insert an element above / on top of / before / in front of / previous the highlighted element, clicking the other button will insert it below / under / after / behind / next the selection. Insertion here is about the same hierarchical level (not children).
Further question: What is the most common term for the entities of such a tree-like data structure? Elements? Nodes? Levels? Layers? Structures? I mean: Which word, if read out a context, is most likely to explain that it is part of a data tree? Like in a sentence as: The function takes two numbers and a … and returns a string.