code: function condense (node) {
    if (node.nodes.length === 1 && node.nodes[0].nodes.length > 0) {
      return condense({
        label: (node.label || '') + node.nodes[0].label,
        nodes: node.nodes[0].nodes
      })
    } else {
      return {
        label: node.label,
        nodes: node.nodes.map(condense)
      }
    }
  }
docs: Merge an archy-node with its single child, but not with a leaf node.
  Keep nodes with zero, two or more childs.
  @access private