Hi Mariamakiling and welcome to GoY. How deep was the soil you added round the tree? It isn't good for trees to bury the stems or trunks as it allows rot to set into the trunk. If you're just covering exposed roots or tops of roots I don't think it will matter, if you've piled earth up against the tree a foot high it might.

A picture always makes it easier to help. Any chance of a photo? You'll be able to add one - or more if they'd help - as you can edit this question.

thanks for your ans...it is a foot high, the garden soil ...oh, such hard work...i have to remove it then

i will try to take pic...

You could make like a doughnut round the tree, so that the soil isn't heaped up against it but there's a higher ring of earth round it. Sorry, it probably took you ages to do.

i have oak trees at the top of my garden ~ they are at least 50 years old and very tall. i havent found their roots yet, they go down very deep but there seems to be enough soil around them ~ ive planted little cyclamen and several bigger shrubs ~ they seem to be ok, just have to be aware that there is not much light underneath in the summer.