Display a table in which the values in first column form one or more trees.
            The table has row with fields that are strings of identifiers/names.
            First convert each row into a row_widget and item_widgets
            that are displayed in a TableTree.
            Each input row shall start with a parent field (field[0])
            that determines the tree hierarchy but that is not displayed on that row.
            The parent widget becomes an attribute of the first child widget.
            Field[1] is the row color, field[2:] contains the row values.
            Top child(s) shall have a parent field value that is blank ('').
            The input table rows shall be in the correct sequence.

def Display_TreeTable(self, table):
        ''' Display a table in which the values in first column form one or more trees.
            The table has row with fields that are strings of identifiers/names.
            First convert each row into a row_widget and item_widgets
            that are displayed in a TableTree.
            Each input row shall start with a parent field (field[0])
            that determines the tree hierarchy but that is not displayed on that row.
            The parent widget becomes an attribute of the first child widget.
            Field[1] is the row color, field[2:] contains the row values.
            Top child(s) shall have a parent field value that is blank ('').
            The input table rows shall be in the correct sequence.
        '''
        parent_names = []
        hierarchy = {}
        indent_level = 0
        widget_dict = {}  # key, value = name, widget
        for row in table:
            parent_name = row[0]
            row_color = row[1]
            child_name = row[2]
            row_widget = gui.TableRow(style={'background-color': row_color})
            # Determine whether hierarchy of sub_sub concepts shall be open or not
            openness = 'true'
            row_widget.attributes['treeopen'] = openness
            # widget_dict[child_name] = row_widget
            for index, field in enumerate(row[2:]):
                # Determine field color
                field_color = '#ffff99'
                row_item = gui.TableItem(text=field,
                                         style={'text-align': 'left',
                                                'background-color': field_color})
                row_widget.append(row_item, field)
                if index == 0:
                    row_item.parent = parent_name
                    child_id = row_item

            # The root of each tree has a parent that is blank ('').
            # Each row with childs has as attribute openness, which by default is 'true'.
            # The fields can be given other attributes, such as color.

            # Verify whether the parent_name (child.parent)
            # is present or is in the list of parent_names.
            print('parent-child:', parent_name, child_name)
            if parent_name == '':
                hierarchy[child_name] = 0
                parent_names.append(child_name)
                target_level = 0
            elif parent_name in parent_names:
                hierarchy[child_name] = hierarchy[parent_name] + 1
                target_level = hierarchy[child_name]
            else:
                # Parent not in parent_names
                print('Error: Parent name "{}" does not appear in network'
                      .format(parent_name))
                return
            print('indent, target-pre:', indent_level, target_level,
                  parent_name, child_name)
            # Indentation
            if target_level > indent_level:
                self.tree_table.begin_fold()
                indent_level += 1
            if target_level < indent_level:
                while target_level < indent_level:
                    indent_level += -1
                    self.tree_table.end_fold()
            print('indent, target-post:', indent_level, target_level,
                  parent_name, child_name)
            if child_name not in parent_names:
                parent_names.append(child_name)
            self.tree_table.append(row_widget, child_name)