The mission is to save the Verdorato. It will be necessary to retrieve Ortican, going to the Rock of the Crow, and, subsequently, returning the Dagger to Danica, it will be necessary to go to the Sanctuary of the Ancient Glimmer, to take the sap 

 Sin, however, that no one will say that the tree will be killed, along with the pilgrims.
  By hitting the tree with the dagger, we will get the sap but, the Spriggan will be released, which will be intent on killing everyone . 

Is there any other way? Yes there is

The first thing to do is to find the Sanctuary of the Ancient Glimmer. You don't need a mission to do this

If not done, we take the mission from Danica, and retrieve Ortican from Hagraven's Nest to the Raven's Rock

 In this area, it is very useful to eliminate the 4 Witches placed to protect the Hagraven . They will be the ones to sound the alarm. Eliminate them using Stealth as much as possible. Make sure you are always in the shelter of the Hagraven Fireballs.

Recovered Ortican, return to Danica, you will witness a dialogue with a certain Maurice

At the end of the dialogue, Maurice will ask you to be able to follow you to the Sanctuary, and if you have discovered the place earlier, accept

If Maurice doesn't ask you anything, you can talk to him.

The usefulness of discovering the Sanctuary first is that, due to the poor general AI, Maurice will tend to attack anyone, making it practically impossible for him to arrive alive at the Sanctuary.

Exit the temple, open the map and teleport to the Shrine of the Ancient Glimmer with Maurice . It's the only way to get him alive and complete the mission in style.
Equip yourself with the Ortican, go up the stairs, hit the roots and reach the tree. DON'T HIT IT

If he hasn't followed you, go back to Maurice to start the dialogue

Maurice will tell you that it is not necessary to kill the tree at all

He knows another way: prayer. At the end of the plea, we will be given a sapling, take it and bring it to Danica

By doing so, we would have obtained what we need: to save the Verdorato and the pilgrims.  Go back to Danica, give her the sapling, and tell him what Maurice told us: It is better to renew than to keep