A $k$-tree is a graph obtained by starting with a $k+1$-clique and repeatedly attaching a $k+1$-clique to the graph along a $k$-clique. A tree is then a $1$-tree in this definition.
Is there anything known about the problem of, given a complete graph on $n$ vertices with edge weights, finding a $k$-tree with $n$ vertices which minimizes the sum of the edge weights of this $k$-tree? For example, is this NP-hard if $k$ is fixed?