var kruskal = require('ngraph.kruskal');
// graph is an instance of ngraph.graph
var tree = kruskal(graph);

// Tree is array of edges that constitute minimum spanning tree (MSP).
assert(Array.isArray(tree));

// Each edge of the MSP is an edge of the graph:
var treeEdge = tree[0];
assert(
  graph.getLink(treeEdge.fromId, treeEdge.toId)
);