i'm trying to replace a field in a treeview ... help me please

 <record model="ir.ui.view" id="view_task_form2_inherited">

<field name="name">project.task.form.inherited</field>

<field name="model">project.task</field>

<field name="inherit_id" ref="project.view_task_form2" />

<field name="arch" type="xml">

<field name="project_id" position="attributes">

<attribute name="on_change">onchange_project(project_id)</attribute>

</field>

<field name="tag_ids" position="after">

<field name="analytic_account_id" invisible="1"/>

<field name="progress" widget="progressbar"

groups="project.group_time_work_estimation_tasks"/>

</field>

<xpath expr="//notebook/page[@name='description_page']" position="after">

<page string="Timesheets" groups="project.group_tasks_work_on_tasks,project.group_time_work_estimation_tasks">

<field name="timesheet_ids" groups="project.group_tasks_work_on_tasks" context="{'default_account_id' : analytic_account_id, 'default_is_timesheet' : 1}">

<tree editable="top" string="Timesheet Activities">

<field name="date"/>

<field name="user_id" required="1"/>

<field name="name"/>

<field name="account_id"/>

<field name="unit_amount" string="Duration" sum="Total time" widget="float_time"/>

<field name="is_timesheet" invisible="1"/>

</tree>

</field>

<group>

<group class="oe_subtotal_footer oe_right" name="project_hours" groups="project.group_time_work_estimation_tasks">

<field name="effective_hours" widget="float_time" groups="project.group_time_work_estimation_tasks"/>

<field name="remaining_hours" widget="float_time" class="oe_subtotal_footer_separator" groups="project.group_time_work_estimation_tasks"/>

</group>

</group>

</page>

</xpath>

</field>

</record>

i want add new field inside "timesheet_ids", 

this is my custom script on _view.xml

        <record id="project_task_view_form" model="ir.ui.view">

<field name="name">project.task.view.form</field>

<field name="model">project.task</field>

<field name="inherit_id" ref="project.view_task_form2"/>

<field name="arch" type="xml">

<xpath expr="/notebook/page[@name='description_page']" position="before">

<page string="Timesheets" groups="project.group_tasks_work_on_tasks,project.group_time_work_estimation_tasks">

<field name="timesheet_ids" groups="project.group_tasks_work_on_tasks" context="{'default_account_id' : analytic_account_id, 'default_is_timesheet' : 1}">

<tree editable="top" string="Timesheet Activities">

<field name="date"/>

<field name="user_id" required="1"/>

<field name="name"/>

<field name="unit_amount" string="Duration" sum="Total time" widget="float_time"/>

<field name="is_timesheet" invisible="1"/>

<field name="invoiceable_analytic_line"/>

</tree>

</field>

</page>

</xpath>

</field>

</record>

but it's not work, why ? please help me and give me solution

Thanks

Aziz Adi Nugroho from Indonesia