code: function() {
          var me = this,
              picker = new Ext.tree.Panel({
                  shrinkWrapDock: 2,
                  store: me.store,
                  floating: true,
                  displayField: me.displayField,
                  columns: me.columns,
                  minHeight: me.minPickerHeight,
                  maxHeight: me.maxPickerHeight,
                  manageHeight: false,
                  shadow: false,
                  listeners: {
                      scope: me,
                      itemclick: me.onItemClick
                  },
                  viewConfig: {
                      listeners: {
                          scope: me,
                          render: me.onViewRender
                      }
                  }
              }),
              view = picker.getView();
  
          if (Ext.isIE9 && Ext.isStrict) {
              // In IE9 strict mode, the tree view grows by the height of the horizontal scroll bar when the items are highlighted or unhighlighted.
              // Also when items are collapsed or expanded the height of the view is off. Forcing a repaint fixes the problem.
              view.on({
                  scope: me,
                  highlightitem: me.repaintPickerView,
                  unhighlightitem: me.repaintPickerView,
                  afteritemexpand: me.repaintPickerView,
                  afteritemcollapse: me.repaintPickerView
              });
          }
          return picker;
      }
docs: Creates and returns the tree panel to be used as this field's picker.