Please find code here :-

=> give class name like a "text-right","text-center" or "text-left" (for alignment)
<tree>
<field name="your field name" class="text-right" />
</tree>

OR

=> give inline style to the field inside tree view like below.

<tree>
<field name="your field name" style="text-align: {left/right/center};" />
</tree>

thank you @Jainesh Shah for reply, i used as :
<field name="employee_age" style="text-align: center;" />
but nothing changed, it is an integer type field and still showing Right Aligned (both column header and column values).
regards

please ignore my previous reply, mistakenly i entered the given code in form view, now i am entering in tree view and it is showing errors while i am upgrading the app which i can't understand.
my code is:
<tree string="Employees">
<field name="name"/>
<field name="employee_age" style="text-align:center;"/>
</tree>
regards

this works (thanks a bunch):
<field name="employee_age" class="text-center"/>
but no effect on column header... how i can align column headers separately? as we want all column headers in center but align column values left/right/center as requied?
regards