from PyQt5 import QtWidgets, uic
import psycopg2

class MyWindow(QtWidgets.QWidget):
    def __init__(self, parent=None):
        QtWidgets.QWidget.__init__(self, parent)
        uic.loadUi("MyForm.ui", self)
        self.btnLoad.clicked.connect(self.on_click_load)
  
    def on_click_load(self):
        self.lineEdit.setText("Хабля")
        
        conn = psycopg2.connect(dbname='TEST1', user='postgres', password='1123581321', host='localhost')
        cursor = conn.cursor()
        tree = self.lineEdit.text()
        
        cursor.execute(
            'INSERT INTO table2(num, "Tree") VALUES(444, '" + tree + "')')    
        conn.commit()
        conn.close()
if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    window = MyWindow()
    window.show()
    sys.exit(app.exec_())