All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
You are required to pay a value equivalent to the branch that you cut. Scholars decided that cutting a big tree necessitates offering a cow and that cutting a small one necessitates offering a sheep. Reliable and trustworthy people should evaluate the damage that occurred to the tree due to its branch being cut and then decide what should be paid as compensation. In Al-Mughni, Ibn Qudaamah said, "He is liable to offer a cow when the tree is big, and a sheep if it is small. As for grass, its value should be paid, and regarding tree's branches, the value of the cut part is due in this case."
If you can not find those who can evaluate the damage, then you have to be cautious and pay even more in order to absolve yourself of liability. The sum that you pay should be given to the poor of the Sacred Precincts of Mecca.
As for entering Mecca without assuming ihram by one who intends to perform the Hajj, he is required to go back to the meeqat (place where one should assume ihram) where he has to assume his ihram and he is not required to do anything else. In case of assuming ihram after having passed the meeqat, one's Hajj is valid and he is required to offer a sacrificial animal. If he fails to go back to the meeqat without a valid excuse, then he is deemed guilty. In Al-Mughni, Ibn Qudaamah said:
Whoever passes the meeqat without assuming ihram while he intends to perform Hajj has to go back to the meeqat again, if he is able, in order to assume ihram. That is applicable regardless of whether person knows the prohibition or not. As far as I know, the scholars unanimously agree that the person is liable for nothing in case he returns to assume ihram from there. If he assumes ihram after having passed the meeqat, then he is required to offer a sacrificial animal whether he returned to the meeqat or not.
Allaah Knows best.