Binary search tree code giving out of resources error - c++

Question

I was trying to create a binary search tree with insert, search and remove functions but when run, the program throwing an error " Killed exit status 137 -- Out Of Resources --" ,
#include <vector>
using namespace std;
class BST
{
public:
int value;
BST *left;
BST *right;
BST(int val)
{
value = val;
left = nullptr;
right = nullptr;
}
BST& insert(int val)
{
BST *current = this;
while (current != nullptr)
{
if (val < current->value)
{
if (current->left == nullptr)
{
current->left = new BST(val);
break;
}
else
current = current->left;
}
if (val > current->value)
{
if (current->right == nullptr)
{
current->right = new BST(val);
break;
}
else
current = current->right;
}
}
return *this;
}
bool contains(int val)
{
BST *current = this;
while (current != nullptr)
{
if (val < current->value)
{
current = current->left;
}
else if (val > current->value)
{
current = current->right;
}
else if (val == current->value)
return true;
//else if(current ==nullptr)
//return false;
}
return false;
}
BST& remove(int val)
{
BST *current = this;
BST *parent = nullptr;
while (current != nullptr)
{
if (val < current->value)
{
parent = current;
current = current->left;
}
if (val > current->value)
{
parent = current;
current = current->right;
}
if (val == current->value)
{
if (current->left != nullptr && current->right != nullptr)
{
fnd(current->right);
}
else if (parent == nullptr)
{
if (current->left != nullptr)
{
current->value = current->left->value;
current->right = current->left->right;
current->left = current->left->left;
}
else if (current->right != nullptr)
{
current->value = current->right->value;
current->left = current->right->left;
current->right = current->right->right;
}
else
current = nullptr;
}
else if (parent->left == current)
{
if (current->left != nullptr)
{
parent->left = current->left;
}
else
{
parent->left = current->right;
}
}
else if (parent->right == current)
{
if (current->left != nullptr)
{
parent->right = current->left;
}
else
{
parent->right = current->right;
}
}
break;
}
}
return *this;
}
void fnd(BST *current)
{
BST *trav = current;
BST *parent;
while (trav->left != nullptr)
{
parent = trav;
trav = trav->left;
}
current->value = trav->value;
parent->left = nullptr;
}
};