How come the methyl group (-CH3) is electron donating?

Hi when there is a bond b/w H and C there is a slight charge speration like this

In methyl there are three H so it looks like this

Notice the delta negative charge on carbon this is enough for carbon to "donate electron"

When case is with ter. carbocation the delta negative charge is satisfying positive charge of carbocation stabilizing it so

So it is a +I group