code: function FPTree(supports, _support) {
                      this.supports = supports;
                      this._support = _support;
                      /**
                       * Whether or not the tree has been built
                       */
                      this._isInit = false;
                      /**
                       * Root node of the FPTree
                       */
                      this.root = new fpnode.FPNode();
                      /**
                       * All first nodes (of different items) inserted in the FPTree (Heads of node-links).
                       */
                      this._firstInserted = {};
                      /**
                       * All last nodes (of different items) inserted in the FPTree (Foots of node-links).
                       */
                      this._lastInserted = {};
                  }
docs: FPTree is a frequent-pattern tree implementation. It consists in a compact
  data structure that stores quantitative information about frequent patterns in
  a set of transactions.
  
  @param  {ItemsCount} supports     The support count of each unique items to be inserted the FPTree.
  @param  {number}     support      The minimum support of each frequent itemset we want to mine.