The oak tree needs to be fertilized with Green Fertilizer at 3 to 4 hour intervals, beginning with the 2nd growth burst, which takes place between 6 and 8 hours after planting, depending on the time of day you plant. The oak tree has 5 growth bursts, the first and last of which you cannot fertilize. The period of fertilization with the oak tree lasts from the appearance of green buds at the tips of the branches until the disappearance of the falling leaves that burst from those buds. The entire tree takes about 17 hours to grow fully. The oak tree will attract Eaglairs too.
You must be level 36 to get an Oak Tree, but you can obtain an Oak Tree seed from the mining site at a lower level.