A complete tree is a graph corresponding to a complete 
-ary tree on 
nodes.
Complete trees are implemented in the Wolfram Language as KaryTree[n, k].
Complete Tree
See also
Complete Binary Tree, Complete Ternary TreeExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Complete Tree." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/CompleteTree.html