code: function( node, level ) { // root node is on level 0
              this.levelMaxDim[level] = {
                  width: Math.max( this.levelMaxDim[level]? this.levelMaxDim[level].width: 0, node.width ),
                  height: Math.max( this.levelMaxDim[level]? this.levelMaxDim[level].height: 0, node.height )
              };
              return this;
          }
docs: Used for calculation of height and width of a level (level dimensions)
  @param {TreeNode} node
  @param {number} level
  @returns {Tree}