I managed to add two custom fields to the settings by inheriting res.config.settings in a new module created. The xml page of the same is
<record id="op_product_fast_moving_parts_form" model="ir.ui.view">
<field name="name">Configure Fast Moving Parts</field>
<field name="model">fastmovingparts.config.settings</field>
<field name="arch" type="xml">
<form string="FastMoving">
<header>
<button string="Apply" type="object" name="execute" class="oe_highlight"/>
or
<button string="Cancel" type="object" name="cancel" class="oe_link"/>
</header>
<separator string="Configure Fast Moving Parts"/>
<group name="Configure Fast Moving Parts">
<field string="Minimum Quantity" name="fast_moving_parts_min_qty"/>
</group>
<group>
<field string="Interval" name="fast_moving_parts_chk_interval"/>
</group>
</form>
</field>
</record>
It is updating the settings when clicking on the Apply button.
Here I have one more requirement that I need to open a wizard on clicking Apply button which will display products tree. How can I achieve this?
Thanks in advance