Vertel has developed one module called: 
https://github.com/vertelab/odoo-project_scrum/tree/13.0/project_hierarchy

The module adds a "parent_id" to the project. This allows a hierarchy of projects. 

hierarchy.py

#-*- coding: utf-8 -*-
from openerp import models, fields, api
class hierarchy(models.Model):
    _name = 'hierarchy'
    parent_id = fields.Many2one('hierarchy',string='Superior Level')
    code = fields.Char('Code',required=True)
    name = fields.Char('Name')
    child_ids = fields.One2many('hierarchy', 'parent_id',string='Sub Levels')

hierarchy_view.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>
        <!-- views -->
        <!-- form view -->
        <record id="view_form_hierarchy" model="ir.ui.view">
            <field name="name">hierarchy Form</field>
            <field name="model">hierarchy</field>
            <field name="arch" type="xml">
                <form>
                    <group>
                        <field name="parent_id"/>
                        <field name="code"/>
                        <field name="name"/>
                        <field name="child_ids"/>
                    </group>
                </form>
            </field>
        </record>
        <!-- tree ( tree ) view -->
        <record id="view_tree_hierarchy" model="ir.ui.view">
            <field name="name">hierarchy Tree</field>
            <field name="model">hierarchy</field>
            <field name="field_parent">child_ids</field>
            <field name="arch" type="xml">
                <tree toolbar="1">
                    <field icon="icon" name="code"/>
                    <field name="name"/>
                </tree>
            </field>
        </record>
        <!-- Actions -->
        <record model="ir.actions.act_window" id="action_hierarchy">
            <field name="name">hierarchy</field>
            <field name="type">ir.actions.act_window</field>
            <field name="res_model">hierarchy</field>
            <field name="view_type">tree</field>
            <field name="domain">[('parent_id','=',False)]</field>
        </record>
        <!-- Menu items -->
        <menuitem id="root_hierarchy" name="hierarchy"/>
        <menuitem id="menu_hierarchy" name="Menu" parent="root_hierarchy"/>
        <menuitem id="hierarchy_opcion" name="hierarchy" parent="menu_hierarchy" sequence="20" action="action_hierarchy"/>
    </data>
</openerp>

Did you find the answer to your question ?

I also want to do that (by the way this forum is not that good for resolving issues? There is no answer to your question. The LinkedIn group seems, at first, better for that)

Thanks,

GH