Why are alkyl groups considered as electron donating groups??

In an alkyl group, the carbon is linked to hydrogen atoms. Carbon is more electronegative than hydrogen. Thus, carbon pulls bonded electrons towards itself and acquires a slight extra negative charge (delta-) and correspondingly hydrogen lose hold over bonded electrons and acquires a slight positive charge (indicated by delta +).

Thus, carbon gets a little more electronic charge which the carbon will push towards the group to which it is linked. Thus, alkyl group sre electron donating group.