model.py

company_technologies = db.Table('company_technologies',
                                db.Column('company_id', db.Integer, db.ForeignKey('companies.id')),
                                db.Column('technology_id', db.Integer, db.ForeignKey('technologies.id'))
                                )

class Technology(db.Model):
    __tablename__ = 'technologies'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128), index=True)
    parent_id = db.Column(db.Integer, default=None, nullable=True, index=True)

class Company(db.Model):
    __tablename__ = 'companies'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128), unique=True, index=True)
    technologies = db.relationship('Technology',
                                      secondary=company_technologies,
                                      backref=db.backref('technologies', lazy='dynamic'),
                                      lazy='dynamic')