here i give you example you can try this way:
from odoo import models, fields, api

class SaleOrderLineSubsection(models.Model):

    _name = 'sale.order.line.subsection'

    name = fields.Char(string='Name')

    product_id = fields.Many2one('product.product', string='Product')

    quantity = fields.Float(string='Quantity')

    price_unit = fields.Float(string='Unit Price')

    subtotal = fields.Float(string='Subtotal', compute='_compute_subtotal')

    @api.depends('quantity', 'price_unit')

    def _compute_subtotal(self):

        for subsection in self:

            subsection.subtotal = subsection.quantity * subsection.price_unit

class SaleOrderLine(models.Model):

    _inherit = 'sale.order.line'

    subsection_ids = fields.One2many('sale.order.line.subsection', 'order_line_id', string='Subsections')

    total_subsections = fields.Float(string='Total Subsections', compute='_compute_total_subsections')

    @api.depends('subsection_ids.subtotal')

    def _compute_total_subsections(self):

        for line in self:

            line.total_subsections = sum(sub.subtotal for sub in line.subsection_ids)

    @api.onchange('subsection_ids')

    def _onchange_subsections(self):

        self.price_subtotal = sum(sub.subtotal for sub in self.subsection_ids)